Method of growing group iii nitride crystal, group iii nitride crystal grown thereby, group iii nitride crystal growing apparatus and semiconductor device

ABSTRACT

A method of growing a group III nitride crystal grows a group III nitride crystal from a solution in which an alkaline metal, a group III metal and nitrogen are dissolved, and includes, in the solution, a material which increases solubility of the nitrogen into the solution.

BACKGROUND OF THE INVENTION

This application claims the benefit of Japanese Patent Applications No.2003-019716 filed Jan. 29, 2003, No. 2003-071302 filed Mar. 17, 2003,No. 2003-081836 filed Mar. 25, 2003, No. 2004-011536 filed Jan. 20,2004, No. 2004-013562 filed Jan. 21, 2004, and No. 2004-012906 filedJan. 21, 2004, in the Japanese Patent Office, the disclosures of whichare hereby incorporated by reference.

The present invention generally relates to methods of growing group IIInitride crystals, group III nitride crystals grown thereby, group IIInitride crystal growing apparatuses and semiconductor devices, and moreparticularly to a method of growing a group III nitride crystal which issuited for use in semiconductor devices such as violet light sourceswhich may be used for writing and/or reading information to and/or fromoptical disks, ultraviolet light sources such as laser diodes and lightemitting diodes, violet light sources which may be used for electronicphotography, and group III nitride electron devices. The presentinvention also relates to a group III nitride crystal and asemiconductor device which are produced using the method of growing thegroup III nitride crystal, and to a group III nitride crystal growingapparatus for growing such a group III nitride crystal.

Existing InGaAlN (group III nitride) devices which are used for violet,blue and green light sources are generally made by using crystal growingmethods such as Metal Organic Chemical Vapor Deposition (MO-CVD) andMolecular Beam Epitaxy (MBE) to grow the InGaAlN (group III nitride)crystal on a sapphire or SiC substrate. But when the sapphire or SiCsubstrate is used, crystal defects increase due to large differencesbetween the coefficient of thermal expansion and the lattice constant ofthe InGaAlN (group III nitride) crystal and the coefficient of thermalexpansion and the lattice constant of the sapphire or SiC substrate. Asa result, device performances of the semiconductor devices having theInGaAlN (group III nitride) grown on the sapphire or SiC substratedeteriorate, thereby making it difficult to extend the serviceable lifeof the light emitting devices, for example, and increasing the powerrequired to operate such semiconductor devices.

Furthermore, in the case of the sapphire substrate which is insulative,it is impossible to draw out the electrodes via the substrate as done inthe conventional light emitting devices. Consequently, when the sapphiresubstrate is used, the electrodes must be drawn out via the group IIInitride crystal layer which is grown on the sapphire substrate. As aresult, the device area becomes large and it becomes difficult to reducethe cost of such semiconductor devices.

In addition, in the case of the semiconductor device having the groupIII nitride crystal grown on the sapphire substrate, it is difficult toseparate the chips by slicing, and it is not easy to obtain a resonatorend surface required by the laser diode by cleavage. For this reason,existing techniques form the resonator end surface by dry etching or,polishes the sapphire substrate to a thickness of 100 μm or less beforeforming the resonator end surface by a process similar to cleavage. Butaccording to these existing techniques, it is impossible to easilyperform the formation of the resonator end surface and the chipseparation in a single process as done in conventional laser diodes.Accordingly, these existing techniques require complex processes andincrease the cost of the semiconductor devices.

In order to solve the problems described above, a technique was proposedto reduce the crystal defects by taking measures such as selectivelygrowing the group III nitride crystal in a lateral direction on thesapphire substrate. According to this proposed technique, it is possibleto reduce the crystal defects compared to a case where a GaN layer isnot selectively grown in the lateral direction on the sapphiresubstrate. However, the above described problems associated with theinsulation and the cleavage caused by the use of the sapphire substratestill exist. Furthermore, this proposed technique requires complexprocesses, and the sapphire substrate warps due to the growing of theGaN layer on the sapphire substrate since sapphire and GaN havedifferent properties. As a result, the cost of the semiconductor devicebecomes high when this proposed technique is employed to make thesemiconductor device.

In order to solve these problems, it is desirable to grow on thesubstrate a layer which is made of the same material as the substrate.In the case described above, it is desirable to grow the GaN layer on aGaN substrate. Hence, research is being made to grow the crystal of bulkGaN by vapor phase deposition, solution growth and the like. However, aGaN substrate having a practical size and a high quality has yet to berealized.

One method of realizing the GaN substrate is proposed in H. Yamane etal., “Preparation of GaN Single Crystals Using a Na Flux”, Chem. Mater.1997, Vol. 9, pp. 413-416. This proposed method grows the GaN crystalusing Na as flux. More particularly, this proposed method uses NaN₃ andGa as raw materials, and seals the raw materials in a nitrogenatmosphere within a stainless steel reaction chamber which has aninternal diameter of 7.5 mm and a length of 100 mm, for example. The GaNcrystal is grown by maintaining the reaction chamber at a temperature of600° C. to 800° C. for 24 hours to 100 hours.

In the case of the proposed method according to H. Yamane et al., the Gacrystal can be grown at a relatively low temperature of 600° C. to 800°C. In addition, the pressure within the reaction chamber is on the orderof approximately 100 kg/cm² and is relatively low. Hence, the growthcondition of this proposed method is practical.

However, the problem with this proposed method is that the size of theobtained crystal is on the order of approximately 1 mm or less andsmall. In other words, the reaction chamber used in H. Yamane et al. isa completely closed system, and the raw materials cannot be suppliedfrom outside the reaction chamber. For this reason, the raw materialsare depleted during the crystal growth and the crystal growth stops,thereby making the size of the obtained crystal on the order ofapproximately 1 mm and small. From the practical point of view, thecrystal having such a small size is unsuited for making thesemiconductor device.

In view of the above, first and second methods were respectivelyproposed in Japanese Laid-Open Patent Applications No. 2001-58900 andNo. 2001-102316.

FIG. 1 is a cross sectional view showing a crystal growing apparatusused by the first method. As shown in FIG. 1, a growth chamber 102 and agroup III metal supply pipe 103 are provided within a reaction chamber101. External pressure is applied to the group III metal supply pipe 103from outside the reaction chamber 101, so as to additionally supply agroup III metal 104 to the reaction chamber 102 which contains flux. Inother words, in order to increase the size of the group III nitridecrystal which is obtained, the first method additionally supplies thegroup III metal 104 when growing the group III nitride crystal.

The group III metal supply pipe 103 has a hole 105. The crystal growingapparatus further includes a pressure applying unit 106, an internalspace 107 of the reaction chamber 101, a nitrogen supply pipe 108, apressure control unit 109, a lower heater 110, and a side heater 111.

On the other hand, the second method may be categorized into a mixingmethod and a fusion method. The mixing method applies external pressureto a molten mixture supply pipe which contains a molten mixture of flux(Na) and group III metal (Ga), so as to additionally supply the moltenmixture to a growth chamber which contains the flux. The fusion methodsupplies an intermetallic compound of flux (Na) and group III metal(Ga), and additionally supplies the group III metal by partial fusion ofthe intermetallic compound.

According to the first and second methods described above, the rawmaterials are additionally supplied during the crystal growth, therebymaking it possible to grow larger crystals.

However, according to the first method, vapor of the flux (Na)concentrates at a low-temperature portion, causing the flux (Na) toadhere on the group III metal supply pipe 103 which has a lowtemperature. As a result, the hole 105 of the group III metal supplypipe 103 may be clogged by the adhered flux (Na). If the temperature ofthe group III metal supply pipe 103 is increased in order to prevent theflux (Na) from adhering thereon, the group III metal reacts with thematerial forming the group III metal supply pipe 103 in a case where thegroup III metal is Ga and the material forming the group III metalsupply pipe 103 is stainless steel, for example. Consequently, the hole105 of the group III metal supply pipe 103 is also clogged when such areaction occurs between the group III metal and the material forming thegroup III metal supply pipe 103.

On the other hand, according to the mixing method of the second method,the flux exists within the molten mixture supply pipe. For this reason,the group III metal and the nitrogen react within the molten mixturesupply pipe and generate a group III nitride, to thereby clog the moltenmixture supply pipe.

According to the fusion method of the second method, if theintermetallic compound is mixed into the flux and partially fused, arapid reaction occurs between the intermetallic compound and thenitrogen, to thereby deteriorate the crystal properties of the group IIInitride which is obtained.

And, according to the mixing and fusion methods of the second method,the solubility of the nitrogen to the molten mixture is small, and thegrowth rate of the group III nitride crystal is low.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful method of growing a group III nitride crystal, groupIII nitride crystal grown thereby, a group III nitride crystal growingapparatus and semiconductor device, in which the problems describedabove are eliminated.

Another and more specific object of the present invention is to providea method of growing a group III nitride crystal, capable of growing ahigh-quality group III nitride crystal having a practically large size,a group III nitride crystal grown thereby, a group III nitride crystalgrowing apparatus, and a semiconductor device which includes a layer ofsuch a group III nitride crystal.

Still another and more specific object of the present invention is toprovide a method of growing a group III nitride crystal, comprisinggrowing a group III nitride crystal from a solution in which an alkalinemetal, a group III metal and nitrogen are dissolved; and including, inthe solution, a material which increases solubility of the nitrogen intothe solution.

Another object of the present invention is to provide a method ofgrowing a group III nitride crystal, comprising preparing, as a solvent,a solution which includes an alkaline metal; and growing a group IIInitride crystal by fusing a group III nitride into the solution andrecrystallizing the group III nitride.

A further object of the present invention is to provide a group IIInitride crystal grown by a process comprising growing a group IIInitride crystal from a solution in which an alkaline metal, a group IIImetal and nitrogen are dissolved; and including, in the solution, amaterial which increases solubility of the nitrogen into the solution,wherein the group III nitride crystal is plate-shaped or columnar.

Another object of the present invention is to provide a group IIInitride crystal growing apparatus comprising a reaction chamber; and asolution container, provided within the reaction chamber, to contain asolution in which an alkaline metal, a group III metal and nitrogen aredissolved, the solution including a material which increases solubilityof the nitrogen into the solution, whereby a group III nitride crystalis grown in the solution within the solution container.

Still another object of the present invention is to provide a method ofgrowing a group III nitride crystal, comprising growing a group IIInitride crystal from a solution in which an alkaline metal, a group IIImetal and nitrogen are dissolved; and including, in the solution, amaterial which controls a ratio of a growth rate of the group IIInitride crystal in a first direction approximately parallel to a c-axisthereof and a growth rate of the group III nitride crystal in a seconddirection approximately perpendicular to the c-axis direction thereof.

A further object of the present invention is to provide a method ofgrowing a group III nitride crystal, comprising growing a group IIInitride crystal from a solution in which an alkaline metal, a group IIImetal and nitrogen are dissolved; and including, in the solution, Liwhich controls a ratio of a growth rate of the group III nitride crystalin a first direction approximately parallel to a c-axis thereof and agrowth rate of the group III nitride crystal in a second directionapproximately perpendicular to the c-axis direction thereof.

Another object of the present invention is to provide a group IIInitride crystal grown by a process comprising growing a group IIInitride crystal from a solution in which an alkaline metal, a group IIImetal and nitrogen are dissolved; and including, in the solution, amaterial which controls a ratio of a growth rate of the group IIInitride crystal in a first direction approximately parallel to a c-axisthereof and a growth rate of the group III nitride crystal in a seconddirection approximately perpendicular to the c-axis direction thereof,wherein the group III nitride crystal is plate-shaped or columnardepending on the material.

Still another object of the present invention is to provide a group IIInitride crystal growing apparatus comprising a reaction chamber; and asolution container, provided within the reaction chamber, to contain asolution in which an alkaline metal, a group III metal and nitrogen aredissolved, the solution including a material which controls a ratio of agrowth rate of the group III nitride crystal in a first directionapproximately parallel to a c-axis thereof and a growth rate of thegroup III nitride crystal in a second direction approximatelyperpendicular to the c-axis direction thereof, whereby a group IIInitride crystal is grown in the solution within the solution container.

A further object of the present invention is to provide a method ofgrowing a group III nitride crystal, comprising fusing a group IIInitride into a solution including an alkaline metal; and recrystallizinga group III nitride crystal at a location different from a locationwhere the group III nitride is dissolved within the solution.

Another object of the present invention is to provide a group IIInitride crystal grown by a process comprising fusing a group III nitrideinto a solution including an alkaline metal; and recrystallizing a groupIII nitride crystal at a location different from a location where thegroup III nitride is dissolved within the solution.

Still another object of the present invention is to provide a group IIInitride crystal growing apparatus, comprising a reaction chamber; and asolution container, provided in the reaction chamber, to contain a groupIII nitride which is dissolved into a solution including an alkalinemetal, whereby a group III nitride crystal is recrystallized at alocation within the solution chamber different from a location where thegroup III nitride is dissolved within the solution.

A further object of the present invention is to provide a method ofgrowing a group III nitride crystal, comprising forming, within areaction chamber, a molten mixture of an alkaline metal and a materialwhich includes a group III metal; growing a group III nitride crystalwhich is made of the group III metal and nitrogen, from the moltenmixture and a material which includes the nitrogen; and controlling atemperature in a vicinity of a surface of the molten mixture and atemperature of a crystal growing region within the molten mixture, sothat the nitrogen dissolves into the molten mixture from the surface andthe group III nitride crystal grows in the crystal growing region whichis other than the surface.

Another object of the present invention is to provide a group IIInitride crystal grown by a process comprising forming, within a reactionchamber, a molten mixture of an alkaline metal and a material whichincludes a group III metal; growing a group III nitride crystal which ismade of the group III metal and nitrogen, from the molten mixture and amaterial which includes the nitrogen; and controlling a temperature in avicinity of a surface of the molten mixture and a temperature of acrystal growing region within the molten mixture, so that the nitrogendissolves into the molten mixture from the surface and the group IIInitride crystal grows in the crystal growing region which is other thanthe surface.

Still another object of the present invention is to provide a group IIInitride crystal growing apparatus comprising a reaction chamber; asolution container, provided within the reaction chamber, to contain amolten mixture of an alkaline metal and a material which includes agroup III metal, so that a group III nitride crystal which is made ofthe group III metal and nitrogen is grown from the molten mixture and amaterial which includes the nitrogen; and means for controlling atemperature in a vicinity of a surface of the molten mixture and atemperature of a crystal growing region within the molten mixture, sothat the nitrogen dissolves into the molten mixture from the surface andthe group III nitride crystal grows in the crystal growing region whichis other than the surface.

A further object of the present invention is to provide a semiconductordevice comprising a substrate made of a group III nitride; and a stackedstructure provided on the substrate, where the stacked structure isselected from a group consisting of a light emitting structure, a lightreceiving structure and a transistor structure, and the substrate ismade by any of the above described methods of growing a group IIInitride crystal.

Other objects and further features of the present invention will beapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing a crystal growing apparatusused by a first method;

FIG. 2 is a cross sectional view showing a first embodiment of a groupIII nitride crystal growing apparatus according to the presentinvention;

FIG. 3 is a perspective view showing a plate-shaped GaN crystal which isobtained by growing a GaN crystal by the group III nitride crystalgrowing apparatus shown in FIG. 2;

FIG. 4 is a cross sectional view showing a second embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 5 is a cross sectional view showing a third embodiment of the groupIII nitride crystal growing apparatus according to the presentinvention;

FIG. 6 is a cross sectional view showing a fourth embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 7 is a diagram showing an amount of dissolved GaN within 1 g of Nawith respect to the temperature;

FIG. 8 is a cross sectional view showing a sixth embodiment of the groupIII nitride crystal growing apparatus according to the presentinvention;

FIG. 9A is a cross sectional view showing a seventh embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 9B is a diagram showing a temperature distribution within areaction chamber of the group III nitride crystal growing apparatusshown in FIG. 9A along a vertical direction;

FIG. 10 is a cross sectional view showing an eighth embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 11 is a cross sectional view showing a ninth embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 12 is a side view showing a columnar GaN crystal which is obtainedby growing a GaN crystal by the group III nitride crystal growingapparatus shown in FIG. 11;

FIG. 13 is a cross sectional view showing group III nitride crystalgrowing apparatus according to the present invention;

FIG. 14 is a cross sectional view showing a plate-shaped GaN crystalwhich is obtained by growing the GaN crystal by the group III nitridecrystal growing apparatus shown in FIG. 13;

FIG. 15 is a cross sectional view showing a plate-shaped GaN crystalwhich is obtained by growing the GaN crystal by the group III nitridecrystal growing apparatus shown in FIG. 13 when no Li is added to thesolution, for comparison purposes;

FIG. 16A is a cross sectional view showing an eleventh embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 16B is a diagram showing a temperature distribution within areaction chamber of the group III nitride crystal growing apparatusshown in FIG. 16A along a vertical direction;

FIG. 17A is a cross sectional view showing a twelfth embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 17B is a diagram showing a temperature distribution within areaction chamber of the group III nitride crystal growing apparatusshown in FIG. 17A along a vertical direction;

FIG. 18A is a cross sectional view showing a thirteenth embodiment ofthe group III nitride crystal growing apparatus according to the presentinvention;

FIG. 18B is a diagram showing a temperature distribution within areaction chamber of the group III nitride crystal growing apparatusshown in FIG. 18A along a vertical direction;

FIG. 19 is a cross sectional view showing a fourteenth embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention;

FIG. 20 is a perspective view showing a columnar GaN crystal which isobtained by growing the GaN crystal by the group III nitride crystalgrowing apparatus shown in FIG. 19;

FIG. 21 is a diagram showing a relationship between a crystal growingtemperature and a crystal growing pressure for the group III nitridecrystal;

FIG. 22 is a perspective view showing a columnar GaN crystal which isobtained by growing the GaN crystal by a fifteenth embodiment of themethod of growing the group III nitride crystal;

FIG. 23 is a perspective view showing a columnar GaN crystal which isobtained by growing the GaN crystal by the fifteenth embodiment of themethod of growing the group III nitride crystal;

FIG. 24 is a perspective view showing a plate-shaped GaN crystal whichis obtained by growing the GaN crystal by a sixteenth embodiment of themethod of growing the group III nitride crystal;

FIG. 25 is a perspective view showing an important part of a firstembodiment of a semiconductor device according to the present invention;

FIG. 26 is a perspective view showing an important part of a secondembodiment of the semiconductor device according to the presentinvention;

FIG. 27 is a cross sectional view showing an important part of thesecond embodiment of the semiconductor device;

FIG. 28 is a cross sectional view showing an important part of a thirdembodiment of the semiconductor device according to the presentinvention;

FIG. 29 is a cross sectional view showing an important part of a fourthembodiment of the semiconductor device according to the presentinvention;

FIG. 30 is a diagram showing an illumination apparatus using a fifthembodiment of the semiconductor device according to the presentinvention;

FIG. 31 is a circuit diagram showing the illumination apparatus shown inFIG. 30;

FIG. 32 is a cross sectional view showing a white LED module within theillumination apparatus shown in FIG. 30; and

FIG. 33 is a cross sectional view showing an important part of the fifthembodiment of the semiconductor device within the white LED module.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description will be given of various embodiments of a method ofgrowing a group III nitride crystal, a group III nitride crystal grownthereby, a group III nitride crystal growing apparatus, and asemiconductor device, according to the present invention, by referringto FIG. 2 and the subsequent figures.

First Embodiment

According to a first embodiment, Na is used as an alkaline metal, and Gais used as a group III metal raw material. Nitrogen gas is used asnitrogen raw material, and Li is added using Li₃N as a raw material, togrow GaN crystals as a group III nitride.

The Na, Ga and Li₃N may be prepared in advance as a molten mixturewithin a solution container, and the nitrogen may be supplied during thecrystal growth by fusion from a vapor phase into the molten mixture, togrow the GaN crystals.

FIG. 2 is a cross sectional view showing a first embodiment of the groupIII nitride crystal growing apparatus, and FIG. 3 is a perspective viewshowing a plate-shaped GaN crystal, that is, a first embodiment of thegroup III nitride crystal, which is obtained by growing the GaN crystalby the group III nitride crystal growing apparatus shown in FIG. 2.

The group III nitride crystal growing apparatus shown in FIG. 2 includesa reaction chamber 11 which accommodates a solution container 12. Thereaction chamber 11 is made of stainless steel and has a closed shape. Asolution 25 including the alkaline metal and the group III metal iscontained within the solution container 12. The solution container 12 isplaced on a holder 26, and contains the solution 25 which is requiredfor the crystal growth of the GaN.

The solution container 12 may be removed from the reaction chamber 11.In this embodiment, the solution container 12 is made of BN.

A gas supply pipe 14 connects to the reaction chamber 11. The gas supplypipe 14 supplies nitrogen (N₂) gas to an internal space 23 within thereaction chamber 11, as the nitrogen raw material, and enablesadjustment of the nitrogen (N₂) gas pressure within the reaction chamber11 from a pressure control unit 16 which connects to a N₂ gas supplypipe 17.

The gas supply pipe 14 branches via a valve 18 so that Ar gas may beintroduced. The Ar gas pressure may be adjusted from a pressure controlunit 19 which connects to an Ar gas supply pipe 20.

The total pressure within the reaction chamber 11 is monitored by apressure gage 22. A heater 13 is arranged on an outer side of thereaction chamber 11. Valves 15 and 21 are provided in the gas supplypipe 14. The reaction chamber 11 may be removed from the group IIInitride crystal growing apparatus at the valve 21, so that only thereaction chamber 11 may be placed into a glove box and worked on by anoperator.

Next, a description will be given of a first embodiment of the method ofgrowing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 2.

First, the reaction chamber 11 is separated from the group III nitridecrystal growing apparatus at the valve 21, and placed into a glove box(not shown) having an Ar atmosphere.

Then, Ga is supplied as the group III metal raw material and Na issupplied as the alkaline metal, into the solution container 12 which ismade of BN. A proportion of Na in the solution 25 is set toNa/(Na+Ga)=0.7.

In addition, Li₃N is supplied as the Li raw material, into the solutioncontainer 12.

Next, the solution container 12 is placed on the holder 26 and setwithin the reaction chamber 11. The reaction chamber 11 is sealed, thevalve 21 is closed, and the inside of the reaction chamber 11 is shutoff from the external atmosphere. The reaction chamber 11 is thenremoved from the glove box, and assembled into the group III nitridecrystal growing apparatus. In other words, the reaction chamber 11 isset at a predetermined position of the group III nitride crystal growingapparatus where the heater 13 is provided, and is connected to the gassupply pipe 14 at the valve 21 so that the reaction chamber 11 mayreceive the N₂ and Ar gases.

The valves 15 and 21 are then opened, to supply the N₂ gas into thereaction chamber 11. In this state, the N₂ gas pressure is set to 3.3MPa by the pressure control unit 16. In this embodiment, this N₂ gaspressure of 3.3 MPa causes the total pressure within the reactionchamber 11 to become 4 MPa when the temperature within the reactionchamber 11 rises to a crystal growth temperature of 775° C., forexample.

Then, the valve 15 is closed, and the valve 18 is opened, to supply theAr gas into the reaction chamber 11. In this state, the Ar gas pressureis set to 6.6 MPa by the pressure control unit 19. In other words, theAr partial pressure within the reaction chamber 11 becomes 3.3 MPa. Inthis embodiment, this Ar gas pressure of 6.6 MPa causes the totalpressure within the reaction chamber 11 to become 8 MPa when thetemperature within the reaction chamber 11 rises to a crystal growthtemperature of 775° C., for example. That is, this Ar gas pressure of6.6 MPa causes the N₂ partial pressure and the Ar partial pressurewithin the reaction chamber 11 to become 4 MPa, respectively.

Thereafter, the valves 18 and 21 are closed. As a result, the reactionchamber 11 is sealed. Then, the heater 13 is turned ON, to raise thetemperature of the reaction chamber 11 and thus the temperature of thesolution 25 from room temperature of 27° C. to the crystal growthtemperature of 775° C. in 1 hour.

As the temperature of the reaction chamber 11 rises, the pressure withinthe sealed reaction chamber 11 increases, and the total pressure withinthe reaction chamber 11 becomes 8 MPa when the crystal growthtemperature of 775° C. is reached. In other words, the N₂ partialpressure and the Ar partial pressure within the reaction chamber 11respectively become 4 MPa.

This state is maintained for 200 hours, before lowering the temperatureto the room temperature. When the reaction chamber 11 was opened afterthe end of the crystal growing process, the present inventors found thatvirtually all of the Ga reacted with the nitrogen, and a large number ofcolorless transparent plate-shaped GaN microcrystals 29 were grown onthe inner walls of the solution container 12. In addition, the presentinventors found that a plate-shaped GaN crystal 30 shown in FIG. 3having a diameter of approximately 5 mm was grown on the surface of thesolution 25. The thickness of the plate-shaped GaN crystal 30 wasapproximately 80 μm or greater. Furthermore, a halfwidth of an X-rayrocking curve with respect to the plate-shaped GaN crystal 30 wasapproximately 45 arcsec to approximately 55 arcsec and narrow, and thedefect density was approximately 10⁶ cm⁻² or less by the etch pitdensity evaluation. Moreover, the plate-shaped GaN crystal 30 had a highresistance and was semiinsulative.

On the other hand, when a similar crystal growing process was performedwithout supplying the Li₃N into the solution 25, the present inventorsfound that there remained Ga which did not react with the N₂. Inaddition, the present inventors found that a small columnar GaN crystaland a large number of thin plate-shaped GaN microcrystals having thec-plane as the principal plane were grown on the inner walls of thesolution container 12. Moreover, a GaN crystal having a diameter ofapproximately 3 mm was grown at the surface of the solution 25. When Liwas mixed into the solution 25, it was found that only a plate-shapedGaN crystal grows and the growth rate of the GaN crystal is high,thereby enabling a larger GaN crystal to be grown within a shorter time.

Therefore, this embodiment of the method of growing a group III nitridecrystal includes growing a group III nitride crystal from a solution inwhich an alkaline metal, a group III metal and nitrogen are dissolved,and including, in the solution, a material which increases solubility ofthe nitrogen into the solution. The material may be selected from agroup consisting of Li, Ca and alkaline earth metals. When the materialis Li, the Li may be included in the solution by adding a nitrogencompound to the solution.

For example, an intermetallic compound of Li and the group III metalfuses at the crystal growing temperature, and will not interfere withthe crystal growth. Hence, it is possible to grow a larger group IIInitride crystal compared to the conventional method, when the sameamount of solution is used.

When the nitrogen compound is used as the Li raw material, it ispossible to reduce the weighing error. In other words, a large weighingerror may occur when weighing the Li because the mass number of Li issmall, but it is possible to reduce the weighing error by using thenitride compound. In addition, no impurity elements will mix into thesolution when the nitrogen compound is used, thereby making it possibleto grow a high-quality group III nitride crystal.

Accordingly, the group III metal and the nitrogen react within thesolution, and the group III nitride crystal of the group III metal andthe nitride is grown. By including, in the solution, the material whichincreases the solubility of the nitrogen into the solution, the groupIII nitride crystal grows within the solution having a high nitrogenconcentration compared to the case where the above material is notdissolved in the solution. For this reason, it is possible to preventthe lack of nitrogen supply which was one cause of the slow growth rate,and accordingly, increase the growth rate. In addition, it is possibleto reduce the nitrogen defect caused by the lack of nitrogen supply, andthus grow the group III nitride crystal having a high quality andsubstantially reduced defects.

The group III nitride may by any suitable compound of nitrogen and oneor more group III metals, such as Ga, Al, In and B. In addition, thealkaline metal may be any suitable alkaline metal including Na and K.

The group III metal raw material is not limited to a particular groupIII material, and any suitable group III material may be used, includinggroup III metals, group III nitrides and materials formed by group IIIelements. Furthermore, the nitrogen raw material Is not limited to aparticular nitrogen material, and any suitable material includingnitrogen may be used. Moreover, the nitrogen compound may be dissolvedinto the solution or, the nitrogen compound gas may be dissolved intothe solution in the vapor state.

Second Embodiment

According to a second embodiment, Na is used as a solvent including analkaline metal, and GaN is used as a group III nitride raw material. TheGaN raw material is dissolved into the Na solvent, to grow GaN crystalsas a group III nitride at a bottom of a solution container.

FIG. 4 is a cross sectional view showing a second embodiment of thegroup III nitride crystal growing apparatus. In FIG. 4, those partswhich are the same as those corresponding parts in FIG. 2 are designatedby the same reference numerals, and a description thereof will beomitted.

The structure of the group III nitride crystal growing apparatus shownin FIG. 4 is basically the same as that of the group III nitride crystalgrowing apparatus shown in FIG. 2, except for the shape of the solutioncontainer 12, the provision of a raw material container 24 which islocated at an upper part of the solution container 12 to contain a GaNraw material 31, and the provision of a cooling rod 27 at a bottomportion of the solution container 12.

According to the group III nitride crystal growing apparatus shown inFIG. 4, it is possible to locally set the bottom of the solutioncontainer 12 to a low temperature, by the cooling rod 27 which isprovided at the bottom portion of the solution container 12.

Next, a description will be given of a second embodiment of the methodof growing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 4.

First, the reaction chamber 11 is separated from the group III nitridecrystal growing apparatus at the valve 21, and placed into a glove box(not shown) having an Ar atmosphere.

Then, the GaN raw material and the Na solvent are supplied to thesolution container 12 which is made of BN. The solution container 12 isplaced on the holder 26 and set within the reaction chamber 11. Thereaction chamber 11 is sealed, the valve 21 is closed, and the inside ofthe reaction chamber 11 is shut off from the external atmosphere. Thereaction chamber 11 is then removed from the glove box, and assembledinto the group III nitride crystal growing apparatus.

In other words, the reaction chamber 11 is set at a predeterminedposition of the group III nitride crystal growing apparatus where theheater 13 is provided, and is connected to the gas supply pipe 14 at thevalve 21 so that the reaction chamber 11 may receive the N₂ and Argases. Thereafter, the N₂ gas is supplied to the reaction chamber 11 soas to prevent the nitrogen from escaping the solution 25 into the vaporphase.

In addition, the Ar gas is supplied to the reaction chamber 11 so as tosuppress evaporation of the Na, and the pressure within the reactionchamber 11 is increased.

In this embodiment, the pressure within the reaction chamber 11 is setto 8 MPa, and the partial pressures of the N₂ and Ar gases respectivelyare 4 MPa. Then, the heater 13 is turned ON to raise the temperature ofthe reaction chamber 11 to 800° C. The GaN crystal is grown bymaintaining the temperature of the reaction chamber 11 at 800° C. for300 hours, and the temperature of the reaction chamber 11 is thereafterreduced to the room temperature. While the temperature of the reactionchamber 11 is maintained at 800° C., the GaN raw material 31 graduallydissolves, and is recrystallized at the bottom of the solution container12 where the temperature is low, to thereby grow the GaN crystal. Whenthe reaction chamber 11 was opened after the end of the crystal growingprocess, it was found that the GaN raw material 31 slightly remains, anda columnar colorless transparent GaN crystal 32 having a length ofapproximately 3 mm and a large number of GaN microcrystals 29 were grownat the bottom of the solution container 12.

Therefore, this embodiment of the method of growing the group IIInitride crystal grows the group III nitride crystal by dissolving agroup III nitride into a solvent which includes the alkaline metal andrecrystallizing the group III nitride. In other words, unlike theconventional method, the group III nitride is used as the raw material,and the group III nitride is dissolved and recrystallized within thesolvent.

Hence, the raw material required for the crystal growth is stablysupplied, and a practically large group III nitride crystal having ahigh quality can be grown.

Conventionally, no suitable solvent existed that dissolved the group IIInitride with a solubility required for the crystal growth. But by usingthe solvent including the alkaline metal, it is possible to dissolve thegroup III nitride with the solubility required for the crystal growth,and to recrystallize the group III nitride to grow the group III nitridecrystal.

Na, K and the like may be used for the alkaline metal included in thesolvent or used as the solvent. However, the alkaline metal of thesolvent is not limited to such, and any suitable material may be useddepending on the group III nitride to be dissolved. For example, whenfusing GaN as the group III nitride, Na may be used as a suitablealkaline metal for the solvent.

The method of recrystallization is also not limited to a particularmethod. For example, a temperature difference may be generated in thesolution, so as to dissolve the group III nitride at the hightemperature portion of the solution and to recrystallize the group IIInitride at the low temperature portion of the solution. Alternatively,it is possible to reduce the temperature of the solution in which thegroup III nitride is dissolved by an amount greater than or equal to thesaturated concentration, so as to cause the recrystallization of thegroup III nitride. Furthermore, the solvent may be evaporated so as tosupersaturate the solvent concentration, so as to cause therecrystallization of the group III nitride.

In order to prevent the nitrogen defect, it is possible to supply thenitrogen into the solution by use a nitrogen raw material, separatelyfrom the nitrogen obtained by the dissolving of the group III nitride.

Third Embodiment

According to a third embodiment, Na is used as a solvent including analkaline metal, and GaN is used as a group III nitride raw material. TheGaN raw material is dissolved into the Na solvent, and the Na solvent isevaporated to form a saturated solution, so as to segregate thesupersaturated GaN and grow GaN crystals as a group III nitride.

FIG. 5 is a cross sectional view showing a third embodiment of the groupIII nitride crystal growing apparatus. In FIG. 5, those parts which arethe same as those corresponding parts in FIG. 2 are designated by thesame reference numerals, and a description thereof will be omitted. Thestructure of the group III nitride crystal growing apparatus shown inFIG. 5 is basically the same as that of the group III nitride crystalgrowing apparatus shown in FIG. 2.

Next, a description will be given of a third embodiment of the method ofgrowing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 5.

The GaN raw material and the Na solvent are supplied to the solutioncontainer 12 and heated to 800° C. so as to dissolve the GaN rawmaterial. The N₂ gas is supplied to the reaction chamber 11 so as toprevent the nitrogen from escaping the solution 25 into the vapor phase,and the N₂ gas is used to set the pressure within the reaction chamber11 to 4 MPa.

The reaction chamber 11 is maintained at 800° C. for 400 hours toevaporate the Na solvent. As the Na solvent evaporates, the solution 25reaches a supersaturated state, and the supersaturated GaN is segregatedto grow the GaN crystals. When the reaction chamber 11 was opened afterthe end of the crystal growing process, it was found that the Na solventis reduced, and a columnar colorless transparent GaN crystal 33 having alength of approximately 3 mm and a large number of GaN microcrystals 29were grown at the bottom of the solution container 12.

Therefore, this embodiment of the method of growing the group IIInitride crystal includes setting a concentration of the group IIInitride within the solution to become greater than or equal to asaturated concentration, so as to segregate the group III nitride andgrow the group III nitride crystal. In other words, the crystalsegregation occurs and the crystal growth can be started when thedissolved concentration of the group III nitride within the solutionbecomes greater than or equal to the saturated concentration.

The method of making the group III nitride concentration within thesolution to become greater than or equal to the saturated concentrationis not limited to a particular method. For example, the temperature ofthe solution may be reduced, so that the group III nitride concentrationbecomes greater than or equal to the saturated concentration.Alternatively, differences in the solubilities of the group III nitridecaused by the temperature of the solution may be effectively utilized togrow the group III nitride crystal.

Fourth Embodiment

According to a fourth embodiment, Na is used as an alkaline metal, andGaN is used as a group III nitride raw material. The GaN raw material isdissolved into the Na solution, and the solution temperature isgradually reduced to form a saturated solution, so as to segregate thesupersaturated GaN and grow GaN crystals as a group III nitride.

FIG. 6 is a cross sectional view showing a fourth embodiment of thegroup III nitride crystal growing apparatus. In FIG. 6, those partswhich are the same as those corresponding parts in FIG. 2 are designatedby the same reference numerals, and a description thereof will beomitted. The structure of the group III nitride crystal growingapparatus shown in FIG. 6 is basically the same as that of the group IIInitride crystal growing apparatus shown in FIG. 2.

Next, a description will be given of a fourth embodiment of the methodof growing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 6.

The GaN raw material and the Na are supplied to the solution container12 and heated, so as to dissolve the GaN raw material.

FIG. 7 is a diagram showing an amount of dissolved GaN within 1 g of Nawith respect to the temperature of the molten mixture, obtained fromexperiments conducted by the present inventors. In FIG. 7, the ordinateindicates the amount of dissolved GaN in mg, and the abscissa indicatesthe temperature in ° C. In addition, a curve I shows a case where no Liis added as in the case of this embodiment, and a curve II shows a casewhere Li is added as in the case of a fifth embodiment which will bedescribed later.

It may be seen from FIG. 7 that the amount of dissolved GaN increasessharply when the temperature becomes 750° C. or greater. In thisembodiment, 15 g of Na is supplied to the solution container 12, and 270mg of GaN raw material is supplied to the solution container 12. Thesolution container 12 is then heated to 800° C. to dissolve the GaN rawmaterial and form a saturated solution. The present inventors have foundthrough experiments that the reaction of the dissolved GaN reaches anequilibrium state in 50 hours to 100 hours. In this embodiment, thesolution container 12 is maintained at 800° C. for 50 hours to dissolvethe GaN raw material. Thereafter, the solution container 12 is cooledfrom 800° C. to 700° C. at a cooling rate of 1° C./hour.

The N₂ gas is supplied to the internal space 23 within the reactionchamber 11 so as to prevent the nitrogen from escaping the solution 25into the vapor phase. In addition, the Ar gas is supplied to theinternal space 23 within the reaction chamber 11 so as to suppressevaporation of the Na, and the pressure within the reaction chamber 11is increased. The pressure within the reaction chamber 11 is set to 8MPa, and the partial pressures of the N₂ and Ar gases respectively are 4MPa.

As the temperature of the solution 25 falls, the solution 25 reaches asupersaturated state, and the supersaturated GaN is segregated to growGaN crystals. When the reaction chamber 11 was opened after the end ofthe crystal growing process, a colorless transparent GaN crystal 34having a size of approximately 2 mm and a large number of GaNmicrocrystals 29 were grown at the bottom of the solution container 12.

Therefore, this embodiment of the method of growing the group IIInitride sets the concentration of the group III nitride within thesolution to become greater than or equal to the saturated concentrationby decreasing a temperature of the solution. In other words, since thesolubility of the group III nitride decreases when the temperature ofthe alkaline metal decreases, the solution reaches the supersaturatedstate as the temperature of the solution decreases, to cause segregationof the group III nitride. Hence, the differences in the solubilities ofthe group III nitride caused by the temperature of the solution areeffectively utilized to grow the group III nitride crystal.

Accordingly, the crystal growth rate can be controlled by thetemperature falling rate of the solution, to thereby control the crystalquality. As a result, it is possible to grow a high-quality group IIInitride crystal.

Fifth Embodiment

According to the fifth embodiment, Na is used as an alkaline metal, andGaN is used as a group III nitride raw material. Furthermore, Li₃N isdissolved as a raw material into the solution of Na and GaN, so as toadd Li which increases the solubility of nitrogen in the solution, thatis, increases the solubility of GaN. The GaN raw material is dissolvedinto the Na solution, and the solution temperature is gradually reducedto form a saturated solution, so as to segregate the supersaturated GaNand grow GaN crystals as a group III nitride.

In other words, this embodiment is similar to the fourth embodimentdescribed above, except that Li is dissolved into the solution.

A fifth embodiment of the group III nitride crystal growing apparatushas the same structure as the fourth embodiment of the group III nitridecrystal growing apparatus shown in FIG. 6.

Next, a description will be given of a fifth embodiment of the method ofgrowing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 6.

This fifth embodiment of the method is basically the same as the fourthembodiment of the method described above, except that Li₃N is dissolvedinto the solution 25 so as to add Li to the solution 25. The addition ofLi increases the solubility of the nitrogen, that is, increases thesolubility of the GaN. Hence, a larger amount of the GaN raw material issupplied compared to the fourth embodiment which does not add Li.

In FIG. 7, the curve II shows the amount of dissolved GaN within 1 g ofNa with respect to the temperature of the molten mixture, for a casewhere 0.1 mmol of Li₃N is dissolved into the molten mixture to add theLi. On the other hand, the curve I shows the amount of dissolved GaNwithin 1 g of Na with respect to the temperature of the molten mixture,for the case where no Li is added.

In this fifth embodiment, 15 g of Na, 1.5 mmol of Li₃N and 375 mg of GaNraw material are supplied to the solution container 12, and maintainedat 800° C. for 50 hours to dissolve the GaN raw material and form asaturated solution. Thereafter, the solution container 12 is cooled from800° C. to 700° C. at a cooling rate of 1° C./hour.

The N₂ gas is supplied to the internal space 23 within the reactionchamber 11 so as to prevent the nitrogen from escaping the solution 25into the vapor phase. In addition, the Ar gas is supplied to theinternal space 23 within the reaction chamber 11 so as to suppressevaporation of the Na, and the pressure within the reaction chamber 11is increased. The pressure within the reaction chamber 11 is set to 8MPa, and the partial pressures of the N₂ and Ar gases respectively are 4MPa.

As the temperature of the solution 25 falls, the solution 25 reaches asupersaturated state, and the supersaturated GaN is segregated to growGaN crystals. When the reaction chamber 11 was opened after the end ofthe crystal growing process, a colorless transparent GaN crystal 34having a size of approximately 3 mm and a large number of GaNmicrocrystals 29 were grown at the bottom of the solution container 12.Compared to the case where no Li is added to the solution 25, the amountof GaN crystal grown increases by an amount corresponding to adifference between the solubilities of GaN for the case where Li isadded and the case where no Li is added, to simultaneously increase theGaN crystal size.

Therefore, this embodiment of the method of growing the group IIInitride selects the material from a group consisting of alkaline metalsother than the alkaline metal included in the solvent. In other words,the material which increases the solubility of the nitrogen into thesolution, increases the solubility of the group III nitride into thesolution. Any suitable material which does not interfere with thecrystal growth may be used for this material which increases thesolubility of the nitrogen into the solution. The material may beselected from a group consisting of Li, Ca and alkaline earth metals. Inaddition, when the material is Li, the Li may be included in thesolution by adding a nitrogen compound to the solution.

Accordingly, it is possible to increase the nitrogen concentrationwithin the solution compared to the conventional method, and increasethe solubility of the group III nitride. Consequently, a larger groupIII nitride crystal may be grown compared to the conventional method,using the same amount of solution. In addition, since the nitrogenconcentration within the solution is increased, it is possible tosuppress the lack of nitrogen supply and accordingly, reduce defectssuch as nitrogen defects. As a result, it is possible to grow ahigh-quality group III nitride crystal.

Sixth Embodiment

A sixth embodiment is similar to the fifth embodiment described above,except that a seed crystal is used to grow the crystals. In other words,Na is used as an alkaline metal, GaN is used as a group III nitride rawmaterial, and Li₃N is dissolved as a raw material into the solution ofNa and GaN so as to add Li which increases the solubility of nitrogen inthe solution, that is, increases the solubility of GaN. The GaN rawmaterial is dissolved into the Na solution, and the solution temperatureis gradually reduced to form a saturated solution, so as to segregatethe supersaturated GaN and grow GaN crystals as a group III nitride.

FIG. 8 is a cross sectional view showing a sixth embodiment of the groupIII nitride crystal growing apparatus. In FIG. 8, those parts which arethe same as those corresponding parts in FIG. 2 are designated by thesame reference numerals, and a description thereof will be omitted. Thestructure of the group III nitride crystal growing apparatus shown inFIG. 8 is basically the same as that of the group III nitride crystalgrowing apparatus shown in FIG. 2, except that a mechanism is providedto hold the seed crystal.

Next, a description will be given of a sixth embodiment of the method ofgrowing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 8.

This embodiment grows the GaN crystal in a manner similar to the fifthembodiment described above, except that a seed crystal 35 is immersed ina vicinity of the surface of the solution 25 so as to grow the GaNcrystal thereat.

The GaN raw material which is dissolved into the solution 25 is drawntowards the surface of the seed crystal 35, and the GaN crystalpreferentially grows on the seed crystal 35. The solution container 12is cooled from 800° C. to 700° C. at a cooling rate of 1° C./hour. Whenthe reaction chamber 11 was opened after the end of the crystal growingprocess, a colorless transparent GaN single crystal 36 having a lengthof approximately 5 mm was grown on the seed crystal 35. The GaN crystal36 which is grown on the seed crystal 35 had a larger crystal sizecompared to the case where no seed crystal is used.

Therefore, this embodiment of the method of growing the group IIInitride crystal selects the material from a group consisting of Li, Caand alkaline earth metals. When the material is Li, the Li may beincluded in the solution by adding a nitrogen compound to the solution.Further, the group III nitride crystal may be grown on a seed crystal.

Hence, it is possible to selectively grow the group III nitride crystalon the seed crystal, and a practically large group III nitride crystalhaving a high quality can be grown at a desired position. Moreover, itis possible to control the crystal orientation of the group III nitridecrystal which is grown, because the seed crystal is used. In otherwords, it is possible to grow a group III nitride crystal having adesired crystal face.

Seventh Embodiment

According to a seventh embodiment, Na is used as an alkaline metal, andGaN is used as a group III nitride raw material. Furthermore, Li₃N isdissolved as a raw material into the solution of Na and GaN, so as toadd Li which increases the solubility of nitrogen in the solution, thatis, increases the solubility of GaN. The GaN raw material is dissolvedinto the Na solution at a high temperature portion, and the GaN issegregated on a seed crystal at a low temperature portion to grow theGaN crystals as a group III nitride.

FIG. 9A is a cross sectional view showing a seventh embodiment of thegroup III nitride crystal growing apparatus, and FIG. 9B is a diagramshowing a temperature distribution within a reaction chamber of thegroup III nitride crystal growing apparatus shown in FIG. 9A along avertical direction. In FIG. 9B, the ordinate indicates the distancealong the vertical direction of the reaction chamber in arbitrary units,and the abscissa indicates the temperature in arbitrary units.

The group III nitride crystal growing apparatus shown in FIG. 9Aincludes a reaction chamber 41 which accommodates a solution container42. The reaction chamber 41 is made of stainless steel and has a closedshape. A solution 59 including the alkaline metal is contained withinthe solution container 42. The solution container 42 contains thesolution 59 which is required for the crystal growth of the GaN.

The solution container 42 may be removed from the reaction chamber 41.In this embodiment, the solution container 42 is made of BN.

A gas supply pipe 49 connects to the reaction chamber 41. The gas supplypipe 49 supplies N₂ gas to an internal space 45 within the reactionchamber 41, as the nitrogen raw material, and enables adjustment of theN₂ gas pressure within the reaction chamber 41 from a pressure controlunit 53.

The gas supply pipe 49 branches via a valve 55 so that Ar gas may beintroduced to suppress evaporation of the alkaline metal. The Ar gaspressure may be adjusted from a pressure control unit 56.

The Ar gas is mixed as an inert gas to suppress the evaporation of thealkaline metal and to independently control the pressure of the N₂ gas.Hence, it is possible to perform the crystal growing process with a highcontrollability.

The total pressure within the reaction chamber 41 is monitored by apressure gage 51. An upper heater 43 and a lower heater 44 are arrangedon an outer side of the reaction chamber 41. Each of the upper and lowerheaters 43 and 44 can be controlled to a desired temperature. Valves 52and 50 are provided in the gas supply pipe 49. The reaction chamber 41may be removed from the group III nitride crystal growing apparatus atthe valve 50, so that only the reaction chamber 41 may be placed into aglove box and worked on by an operator.

A buffer 46 is provided within the solution container 42, in order tosuppress convection of the solution 59 and to generate a temperaturegradient.

Next, a description will be given of a seventh embodiment of the methodof growing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 9A.

First, the reaction chamber 41 is separated from the group III nitridecrystal growing apparatus at the valve 50, and placed into a glove box(not shown) having an Ar atmosphere.

Then, GaN is supplied as the group III nitride raw material, Na issupplied as the alkaline metal, and Li₃N is supplied, into the solutioncontainer 42 which is made of BN. The Na within the solution container42 is fused, and a GaN seed crystal 48 which hangs from an upper portionof the solution container 42 is held at a predetermined position withinthe solution 59.

Next, the solution container 42 is set within the reaction chamber 41.The reaction chamber 41 is sealed, the valve 50 is closed, and theinside of the reaction chamber 41 is shut off from the externalatmosphere.

Since the series of operations are carried out within the glove boxunder the Ar gas atmosphere, the inside of the reaction chamber 41 isfilled with the Ar gas. The reaction chamber 41 is then removed from theglove box, and assembled into the group III nitride crystal growingapparatus. In other words, the reaction chamber 41 is set at apredetermined position of the group III nitride crystal growingapparatus where the upper and lower heaters 43 and 44 are provided, andis connected to the gas supply pipe 49 at the valve 50 so that thereaction chamber 41 may receive the N₂ and Ar gases. Then, the upper andlower heaters 43 and 44 are turned ON, to raise the temperature of thereaction chamber 41 and thus the temperature of the solution 59, to apredetermined crystal growing temperature.

The lower heater 44 is set to a dissolving temperature of a GaN rawmaterial 47. On the other hand, the upper heater 43 is set to atemperature which is lower than that at a portion where the GaN rawmaterial 47 exists. More particularly, the upper heater 43 is set to acrystal growing temperature at which the GaN seed crystal 48 grows. Inthis embodiment, the portion where the GaN raw material 47 exists is setto 850° C., and the portion where the GaN seed crystal 48 grows is setto 775° C.

The valves 50 and 55 are then opened, to supply the Ar gas from an Argas supply pipe 57 to the reaction chamber 41 via the gas supply pipe49. The pressure within the reaction chamber 41 is adjusted by thepressure control unit 56, and the valve 55 is closed after setting thetotal pressure within the reaction chamber 41 to 4 MPa.

Thereafter, the valve 52 is opened, to supply the N₂ gas from a N₂ gassupply pipe 54 to the reaction chamber 41 via the gas supply pipe 49.The pressure within the reaction chamber 41 is adjusted by the pressurecontrol unit 53, so that the total pressure within the reaction chamber41 is 8 MPa. In other words, the N₂ partial pressure within the internalspace 45 of the reaction chamber 41 is 4 MPa.

This state is maintained for 400 hours to carry out the crystal growingprocess, and the temperature of the reaction chamber 41 is then reducedto the room temperature. When the reaction chamber 41 was opened afterreducing the gas pressure within the reaction chamber 41, it was foundthat a colorless transparent GaN single crystal 58 having a length ofapproximately 10 mm was grown on the seed crystal 48.

Therefore, this embodiment of the method of growing the group IIInitride crystal also selects the material from a group consisting of Li,Ca and alkaline earth metals. When the material is Li, the Li may beincluded in the solution by adding a nitrogen compound to the solution.Further, the group III nitride crystal may be grown on a seed crystal.

Hence, it is possible to selectively grow the group III nitride crystalon the seed crystal, and a practically large group III nitride crystalhaving a high quality can be grown at a desired position. Moreover, itis possible to control the crystal orientation of the group III nitridecrystal which is grown, because the seed crystal is used. In otherwords, it is possible to grow a group III nitride crystal having adesired crystal face.

Eighth Embodiment

According to an eighth embodiment, Na is used as an alkaline metal, andGa is used as a group III metal raw material. Nitrogen gas is used asnitrogen raw material, and Li is added using Li₃N as a raw material, togrow GaN crystals as a group III nitride.

The Na, Ga and Li₃N may be prepared in advance as a molten mixturewithin a solution container, and the nitrogen may be supplied during thecrystal growth by fusion from a vapor phase into the molten mixture, togrow the GaN crystals.

FIG. 10 is a cross sectional view showing an eighth embodiment of thegroup III nitride crystal growing apparatus. In FIG. 10, those partswhich are the same as those corresponding parts in FIG. 2 are designatedby the same reference numerals, and a description thereof will beomitted. An eighth embodiment of the group III nitride crystal, which isobtained by growing the GaN crystal by the group III nitride crystalgrowing apparatus shown in FIG. 10, becomes the same as the colorlesstransparent plate-shaped GaN crystal 30 shown in FIG. 3.

In this embodiment, the crystal growing process may be carried out undersimilar conditions as those of the first embodiment described above,except that the Li is added to the solution as a material which controlsthe ratio of growth rates of the group III nitride crystal in twoapproximately perpendicular directions.

In other words, this embodiment of the method of growing the group IIInitride crystal comprises growing a group III nitride crystal from asolution in which an alkaline metal, a group III metal and nitrogen aredissolved, and including, in the solution, a material which controls aratio of a growth rate of the group III nitride crystal in a firstdirection approximately parallel to a c-axis thereof and a growth rateof the group III nitride crystal in a second direction approximatelyperpendicular to the c-axis direction thereof.

Materials such as Li make the growth rate of the group III nitridecrystal in the second direction higher than that in the first direction.In this case, it is possible to grow the plate-shaped group III nitridecrystal 30 which extends in a planar manner along the second directionwhich is approximately perpendicular to the c-axis direction thereof.

On the other hand, materials such as Ni, Mn, Fe and Co, which aretransition metals, make the growth rate of the group III nitride crystalin the first direction higher than that in the second direction. In thiscase, it is possible to grow a columnar group III nitride crystal whichis elongated along the first direction which is approximately parallelto the c-axis direction thereof.

Of course, the material which controls the ratio of the growth rates inthe first and second direction may control the ratio so that the twogrowth rates are the same.

Accordingly, it is possible to control the form or shape of the groupIII nitride crystal that is grown.

Furthermore, when the Li is added to the solution, the present inventorsconfirmed that the group III nitride crystal which is grown has a largeresistance on the order of approximately several MΩ, even when nospecial impurity is mixed into the solution.

The following shows a comparison of the properties of the group IIInitride crystals which are grown using the solution without Li(additive) and the solution with Li (additive), where “XRC FWHM”indicates a halfwidth of an X-ray rocking curve with respect to thegrown group III nitride crystal, and “EPD” indicates the defect densityobtained by the etch pit density evaluation.

Case 1: Without Li (Additive)

Conductivity type: n-type

Resistivity: 0.04 Ωcm

Carrier Concentration: 1 to 2×10¹⁸ cm⁻³XRC FWHM (0002): 45 to 55 arcsecEPD: ≦10⁶ cm⁻²

Case 2 (Eighth Embodiment): With Li (Additive)

Conductivity type: Semi-insulative

Resistivity: 10⁴ Ωcm Carrier Concentration: - - -

XRC FWHM (0002): 45 to 55 arcsecEPD: ≦10⁶ cm⁻²

Ninth Embodiment

According to a ninth embodiment, Na is used as an alkaline metal, and Gais used as a group III metal raw material. Nitrogen gas is used asnitrogen raw material, and Ni is added, to grow GaN crystals as a groupIII nitride.

The Na, Ga and Ni may be prepared in advance as a molten mixture withina solution container, and the nitrogen may be supplied during thecrystal growth by fusion from a vapor phase into the molten mixture, togrow the GaN crystals.

FIG. 11 is a cross sectional view showing a ninth embodiment of thegroup III nitride crystal growing apparatus. In FIG. 11, those partswhich are the same as those corresponding parts in FIG. 10 aredesignated by the same reference numerals, and a description thereofwill be omitted. FIG. 12 is a side view showing a columnar GaN crystal,that is, a ninth embodiment of the group III nitride crystal, which isobtained by growing the GaN crystal by the group III nitride crystalgrowing apparatus shown in FIG. 11.

In this embodiment, the crystal growing process may be carried out undersimilar conditions as those of the eighth embodiment described above,except that the Ni is added to the solution, in place of Li, as amaterial which controls the ratio of growth rates of the group IIInitride crystal in two approximately perpendicular directions.

After the crystal growing process is carried out for 300 hours,colorless transparent columnar GaN crystals 131 having a length of 5 mmalong the c-axis direction were grown on the inner walls of the solutioncontainer 12.

On the other hand, when the Ni is not included in the solution 25 whencarrying out a similar crystal growing process, it was found that acolumnar GaN crystal having a short length along the c-axis and a largenumber of plate-shaped GaN crystals having the c-plane as the principalplane are grown.

The present inventors confirmed through experiments that the growth rateof the GaN crystal in the c-axis direction becomes higher when the Ni ismixed into the solution 25, and that a larger columnar GaN crystal canbe grown within a shorter time compared to the case where the Ni is notmixed into the solution 25.

Accordingly, it is possible to control the columnar shape of the groupIII nitride crystal that is grown. In other words, since the group IIInitride crystal can be grown in an ingot shape, a large number of groupIII nitride substrates can be produced at a low cost by slicing theingot-shaped group III nitride crystal.

Tenth Embodiment

According to a tenth embodiment, Na is used as an alkaline metal, and Gais used as a group III metal raw material. Nitrogen gas is used asnitrogen raw material, and Li is added using Li₃N as a raw material, togrow GaN crystals as a group III nitride.

The Na, Ga and Li₃N may be prepared in advance as a molten mixturewithin a solution container, and the nitrogen may be supplied during thecrystal growth by fusion from a vapor phase into the molten mixture, togrow the GaN crystals.

FIG. 13 is a cross sectional view showing a tenth embodiment of thegroup III nitride crystal growing apparatus. In FIG. 13, those partswhich are the same as those corresponding parts in FIG. 10 aredesignated by the same reference numerals, and a description thereofwill be omitted. FIG. 14 is a cross sectional view showing aplate-shaped GaN crystal, that is, a tenth embodiment of the group IIInitride crystal, which is obtained by growing the GaN crystal by thegroup III nitride crystal growing apparatus shown in FIG. 13. Inaddition, FIG. 15 is a cross sectional view showing a plate-shaped GaNcrystal which is obtained by growing the GaN crystal by the group IIInitride crystal growing apparatus shown in FIG. 13 when no Li is addedto the solution, for comparison purposes.

In this embodiment, the crystal growing process may be carried out undersimilar conditions as those of the eighth embodiment described above,except that the Li is added to the solution as a material which controlsthe ratio of growth rates of the group III nitride crystal in twoapproximately perpendicular directions, and that a plate-shaped GaNcrystal having the c-plane as the principal plane is used as a seedcrystal.

More particularly, the reaction chamber 11 is first separated from thegroup III nitride crystal growing apparatus at the valve 21, and placedinto a glove box (not shown) having an Ar atmosphere.

Then, a plate-shaped GaN crystal having the c-plane as the principalplane, is set in the solution container 12, as a seed crystal 132. Next,Ga is supplied as the group III metal raw material and Na is supplied asthe alkaline metal, into the solution container 12 which is made of BN.A proportion of Na in the solution 25 is set to Na/(Na+Ga)=0.4.

In addition, Li₃N is supplied as the Li raw material, into the solutioncontainer 12.

Next, the solution container 12 is placed on the holder 26 and setwithin the reaction chamber 11. Thereafter, the crystal growing processis carried out similarly to the eighth (or first) embodiment.

After the crystal growing process is carried out for 300 hours, acolorless transparent plate-shaped GaN crystal 133 having a smoothsurface was grown on the seed crystal 132, as shown in FIG. 14.

On the other hand, when the Li is not included in the solution 25 whencarrying out a similar crystal growing process, it was found that a GaNcrystal 134 having a rough surface was grown on the seed crystal 132, asshown in FIG. 15.

Hence, it was confirmed that the plate-shaped GaN crystal 133 having theflat surface is obtained when the Li is mixed into the solution 25.Furthermore, a halfwidth of an X-ray rocking curve with respect to theplate-shaped GaN crystal 133 was approximately 45 arcsec toapproximately 55 arcsec and narrow, and the defect density wasapproximately 10⁶ cm⁻² or less by the etch pit density evaluation.Moreover, the plate-shaped GaN crystal 133 had a high resistance and wassemiinsulative.

The present inventors confirmed through experiments that the growth rateof the GaN crystal in the direction perpendicular to the c-axisdirection becomes higher when the Li is mixed into the solution 25.

Accordingly, it is possible to control the plate shape of the group IIInitride crystal that is grown. In other words, since the group IIInitride crystal can be grown in a plate shape, the plate-shaped groupIII nitride crystal itself can be used as a group III nitride substrate,thereby reducing the production cost of the group III nitride substrate.

Eleventh Embodiment

FIG. 16A is a cross sectional view showing an eleventh embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention, and FIG. 16B is a diagram showing a temperature distributionwithin a reaction chamber of the group III nitride crystal growingapparatus shown in FIG. 16A along a vertical direction. In FIG. 16B, theordinate indicates the distance along the vertical direction of thereaction chamber in arbitrary units, and the abscissa indicates thetemperature in arbitrary units.

The group III nitride crystal growing apparatus shown in FIG. 16Aincludes a reaction chamber 211 which is made of stainless steel and hasa closed shape, and a solution container 212 which is accommodatedwithin the reaction chamber 211. The solution container 212 contains asolution 216 which includes an alkaline metal and is used to grow thegroup III nitride crystal. The solution container 212 may be removedfrom the reaction chamber 211. In this embodiment, the solutioncontainer 212 is made of BN.

An upper heater 213 and a lower heater 214 are provided on the outerside of the reaction chamber 211. Each of the upper and lower heaters213 and 214 can be controlled to an arbitrary temperature.

The reaction chamber 211 can be removed from the group III nitridecrystal growing apparatus. Hence, the reaction chamber 211 may be placedwithin a glove box without releasing the inside of the reaction chamber211 to the atmosphere, and it is possible to work on the reactionchamber 211 within the glove box, such as preparing and setting a rawmaterial within a high purity Ar gas atmosphere within the glove box.For this reason, it is possible to prevent moisture and impurities inthe atmosphere from entering the reaction chamber 211, so that ahigh-quality group III nitride crystal can be grown.

Next, a description will be given of an eleventh embodiment of themethod of growing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 16A.

First, the reaction chamber 211 is removed from the group III nitridecrystal growing apparatus, and placed within a glove box (not shown)having an Ar atmosphere. Then, a GaN raw material 217 is supplied to thesolution container 212 as a group III nitride raw material, and asolution 216 including Na as an alkaline metal is supplied to thesolution container 212. The solution container 212 is set within thereaction chamber 211, and the reaction chamber 211 is sealed, so as toshut off the inside of the reaction chamber 211 from externalatmosphere. The series of operations are carried out within the glovebox having the high purity Ar gas atmosphere, and thus, the inside ofthe reaction chamber 211 is filled with the Ar gas.

Next, the reaction chamber 211 is removed from the glove box andassembled into the group III nitride crystal growing apparatus. In otherwords, the reaction chamber 211 is set at a predetermined position wherethe upper and lower heaters 213 and 214 are provided. The upper andlower heaters 213 and 214 are turned ON to raise the temperature of thereaction chamber 211 to a predetermined crystal growing temperature.More particularly, the lower heater 214 is set to a dissolvingtemperature of the GaN raw material 217, and the upper heater 213 is setto a crystal growing temperature at which the GaN recrystallizes and islower than a portion where the GaN raw material 217 exists. In thisembodiment, the temperature of the portion where the GaN raw material217 exists is set to 850° C., and the crystal growing temperature of theportion where the crystal growth takes place is set to 775° C.

The above described state is maintained for 500 hours, before decreasingthe temperature of the reaction chamber 211 to the room temperature.When the reaction chamber 211 was opened after reducing the gas pressurewithin the reaction chamber 211, it was found that several colorlesstransparent GaN single crystals 218 having a length of approximately 3mm were grown in a recrystallization temperature region within thesolution container 212.

Twelfth Embodiment

FIG. 17A is a cross sectional view showing a twelfth embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention, and FIG. 17B is a diagram showing a temperature distributionwithin a reaction chamber of the group III nitride crystal growingapparatus shown in FIG. 17A along a vertical direction. In FIG. 17B, theordinate indicates the distance along the vertical direction of thereaction chamber in arbitrary units, and the abscissa indicates thetemperature in arbitrary units.

The group III nitride crystal growing apparatus shown in FIG. 17Aincludes a reaction chamber 221 which is made of stainless steel and hasa closed shape, and a solution container 222 which is accommodatedwithin the reaction chamber 221. The solution container 222 contains asolution 226 which includes an alkaline metal and is used to grow thegroup III nitride crystal. The solution container 222 may be removedfrom the reaction chamber 221. In this embodiment, the solutioncontainer 222 is made of BN.

An upper heater 223 and a lower heater 224 are provided on the outerside of the reaction chamber 221. Each of the upper and lower heaters223 and 224 can be controlled to an arbitrary temperature.

The reaction chamber 221 can be removed from the group III nitridecrystal growing apparatus. Hence, the reaction chamber 221 may be placedwithin a glove box without releasing the inside of the reaction chamber221 to the atmosphere, and it is possible to work on the reactionchamber 221 within the glove box, such as preparing and setting a rawmaterial within a high purity Ar gas atmosphere within the glove box.For this reason, it is possible to prevent moisture and impurities inthe atmosphere from entering the reaction chamber 221, so that ahigh-quality group III nitride crystal can be grown.

Next, a description will be given of a twelfth embodiment of the methodof growing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 17A.

First, the reaction chamber 221 is removed from the group III nitridecrystal growing apparatus at a valve 230, and placed within a glove box(not shown) having an Ar atmosphere. Then, a GaN raw material 227 issupplied to the solution container 222 as a group III nitride rawmaterial, and a solution 226 including Na as an alkaline metal issupplied to the solution container 222. The solution container 222 isset within the reaction chamber 221, and the reaction chamber 221 issealed, so as to shut off the inside of the reaction chamber 221 fromexternal atmosphere. The series of operations are carried out within theglove box having the high purity Ar gas atmosphere, and thus, the insideof the reaction chamber 221 is filled with the Ar gas.

Next, the reaction chamber 221 is removed from the glove box andassembled into the group III nitride crystal growing apparatus. In otherwords, the reaction chamber 221 is set at a predetermined position wherethe upper and lower heaters 223 and 224 are provided, and connected atthe valve 230 to a N₂ gas supply pipe 229. The upper and lower heaters223 and 224 are turned ON to raise the temperature of the reactionchamber 221 to a predetermined crystal growing temperature. Moreparticularly, the lower heater 224 is set to a dissolving temperature ofthe GaN raw material 227, and the upper heater 223 is set to a crystalgrowing temperature at which the GaN recrystallizes and is lower than aportion where the GaN raw material 227 exists. In this embodiment, thetemperature of the portion where the GaN raw material 227 exists is setto 850° C., and the crystal growing temperature of the portion where thecrystal growth takes place is set to 775° C.

The valve 230 and a valve 232 are opened to supply the N₂ gas from theN₂ gas supply pipe 229 to the reaction chamber 221. The pressure of theN₂ gas is monitored by a pressure gage 231, and controlled by a pressurecontrol unit 232. Hence, the pressure of the N₂ gas is adjusted by thepressure control unit 232 so that the total pressure within the reactionchamber 221 becomes 4 MPa.

The above described state is maintained for 500 hours, before decreasingthe temperature of the reaction chamber 221 to the room temperature.When the reaction chamber 221 was opened after reducing the gas pressurewithin the reaction chamber 221, it was found that several colorlesstransparent GaN single crystals 228 having a length of approximately 5mm were grown in a recrystallization temperature region within thesolution container 222.

Thirteenth Embodiment

FIG. 18A is a cross sectional view showing a thirteenth embodiment ofthe group III nitride crystal growing apparatus according to the presentinvention, and FIG. 18B is a diagram showing a temperature distributionwithin a reaction chamber of the group III nitride crystal growingapparatus shown in FIG. 18A along a vertical direction. In FIG. 18B, theordinate indicates the distance along the vertical direction of thereaction chamber in arbitrary units, and the abscissa indicates thetemperature in arbitrary units.

The group III nitride crystal growing apparatus shown in FIG. 18Aincludes a reaction chamber 241 which is made of stainless steel and hasa closed shape, and a solution container 242 which is accommodatedwithin the reaction chamber 241. The solution container 242 contains asolution 246 which includes an alkaline metal and is used to grow thegroup III nitride crystal. The solution container 242 may be removedfrom the reaction chamber 241. In this embodiment, the solutioncontainer 242 is made of BN.

A gas supply pipe 249 is connected to the reaction chamber 241, so thatan internal space 245 within the reaction chamber 241 may be filled withN₂ gas and Ar gas for suppressing evaporation of an alkaline metal. TheN₂ gas pressure and the Ar gas pressure within the reaction chamber 241are controllable.

The gas supply pipe 249 branches to a N₂ gas supply pipe 254 via a valve252, and branches to an Ar gas supply pipe 257 via a valve 255. Thepressure within the N₂ gas supply pipe 254 is controllable by a pressurecontrol unit 253, and the pressure within the Ar gas supply pipe 257 iscontrollable by a pressure control unit 256.

The total pressure within the reaction chamber is monitored by apressure gage 251 which is provided on the gas supply pipe 249. The Argas is mixed as an inert gas in order to suppress evaporation of thealkaline metal and to independently control the pressure of the N₂ gas.Hence, a crystal growth with a high controllability is achieved.

An upper heater 243 and a lower heater 244 are provided on the outerside of the reaction chamber 241. Each of the upper and lower heaters243 and 244 can be controlled to an arbitrary temperature.

The reaction chamber 241 can be removed from the group III nitridecrystal growing apparatus. Hence, the reaction chamber 241 may be placedwithin a glove box without releasing the inside of the reaction chamber241 to the atmosphere, and it is possible to work on the reactionchamber 241 within the glove box, such as preparing and setting a rawmaterial within a high purity Ar gas atmosphere within the glove box.For this reason, it is possible to prevent moisture and impurities inthe atmosphere from entering the reaction chamber 241, so that ahigh-quality group III nitride crystal can be grown.

Next, a description will be given of a thirteenth embodiment of themethod of growing the group III nitride crystal according to the presentinvention, which grows GaN, by the group III nitride crystal growingapparatus shown in FIG. 18A.

First, the reaction chamber 241 is removed from the group III nitridecrystal growing apparatus at a valve 250, and placed within a glove box(not shown) having an Ar atmosphere. Then, a GaN raw material 247 issupplied to the solution container 242 as a group III nitride rawmaterial, and a solution 246 including Na as the alkaline metal issupplied to the solution container 242. In this embodiment, plate-shapedcrystals having an approximately stoichiometry composition, grown withina molten mixture of Na and Ga under a N₂ pressure of 5 MPa, were used asthe GaN raw material 247.

Thereafter, the Na within the solution container 242 is fused, and a GaNseed crystal 248 is hanged from an upper portion of the solutioncontainer 242 and held at a predetermined position within a Na solution246. The solution container 242 is set within the reaction chamber 241,and the reaction chamber 241 is sealed, so as to shut off the inside ofthe reaction chamber 241 from external atmosphere. The series ofoperations are carried out within the glove box having the high purityAr gas atmosphere, and thus, the inside of the reaction chamber 241 isfilled with the Ar gas.

Next, the reaction chamber 241 is removed from the glove box andassembled into the group III nitride crystal growing apparatus. In otherwords, the reaction chamber 241 is set at a predetermined position wherethe upper and lower heaters 243 and 244 are provided, and connected atthe valve 250 to the gas supply pipe 249. The upper and lower heaters243 and 244 are turned ON to raise the temperature of the reactionchamber 241 to a predetermined crystal growing temperature. Moreparticularly, the lower heater 244 is set to a dissolving temperature ofthe GaN raw material 247, and the upper heater 243 is set to a crystalgrowing temperature at which the GaN seed crystal 248 grows and is lowerthan a portion where the GaN raw material 247 exists. In thisembodiment, the temperature of the portion where the GaN raw material247 exists is set to 850° C., and the crystal growing temperature of theportion where the crystal growth of the GaN seed crystal 248 takes placeis set to 775° C.

The valve 250 and the valve 255 are opened to supply the Ar gas from theAr gas supply pipe 257, and the pressure is controlled by the pressurecontrol unit 256 to control the total pressure within the reactionchamber 241 to 4 MPa, before closing the valve 255. Then, the valve 252is opened to supply the N₂ gas from the N₂ gas supply pipe 254, and thepressure is controlled by the pressure control unit 253 to control thetotal pressure within the reaction chamber 241 to 8 MPa. In other words,the Ar partial pressure and the N₂ partial pressure in the internalspace 245 within the reaction chamber 241 are respectively set to 4 MPa.

The above described state is maintained for 500 hours, before decreasingthe temperature of the reaction chamber 241 to the room temperature.When the reaction chamber 241 was opened after reducing the gas pressurewithin the reaction chamber 241, it was found that a colorlesstransparent GaN single crystal 258 having a length of approximately 10mm was grown on the GaN seed crystal 248 within the solution container242.

Therefore, according to the eleventh through thirteenth embodiments, themethod of growing a group III nitride crystal, comprises dissolving agroup III nitride into a solution including an alkaline metal, andrecrystallizing a group III nitride crystal at a location different froma location where the group III nitride is dissolved within the solution.In other words, when the group III nitride is held at a predeterminedtemperature within the solution which includes the alkaline metal, thegroup III nitride dissolves into the solution with a certain solubility.The dissolved group III nitride recrystallizes at a location where thesupersaturation becomes large, such as a location where the temperatureis low and a location where the nitrogen concentration is high. Hence,the group III nitride raw material is dissolved to recrystallize andgrow the group III nitride crystal.

The group III nitride may be selected from group III metals such as Ga,Al and In. In addition, the group III nitride may be selected fromcompounds of nitrogen and one or a plurality of such group III metals.On the other hand, the alkaline metal may be selected from Na, K orother suitable alkaline metals. It is possible to dissolve anothermaterial within the solution which includes the alkaline metal. Forexample, the solution which includes the alkaline metal may be doped byfusing an n-type impurity or a p-type impurity.

According to the eleventh through thirteenth embodiments, the rawmaterial required for the crystal growth is stably supplied without thepossibility of clogging the supply pipe, and a practically large groupIII nitride crystal having a high quality can be grown.

It is desirable that the solution contacts the N₂ gas. In other words,the solution into which the group III nitride is dissolved, desirablycontacts the N₂ gas having a predetermined partial pressure at agas-liquid interface. When the group III nitride dissolves into thesolution, the nitrogen generated by the decomposition of the group IIInitride assumes a gaseous state and the nitrogen concentration withinthe solution decreases. Accordingly, the amount of nitrogen raw materialbecomes insufficient compared to the group III raw material. For thisreason, the predetermined N₂ partial pressure is applied on the solutionand the N₂ partial pressure is adjusted, so as to present lack of thenitrogen raw material. In addition, by controlling the nitrogenconcentration within the solution, it is possible to control the crystalgrowth rate and the crystal quality when growing the group III nitridecrystal.

Therefore, when the solution which includes the alkaline metal contactsthe N₂ gas, it is possible to suppress escaping of the nitrogen from thesolution, to thereby prevent the lack of the nitrogen raw material andgrow a high-quality group III nitride crystal. In addition, it ispossible to control the nitrogen concentration within the solution bycontrolling the N₂ partial pressure in the vapor phase, and the groupIII nitride crystal can be grown by controlling the crystal growth rateand the crystal quality. Consequently, it is possible to grow apractically large group III nitride crystal having a high quality.

The group III nitride which is dissolved into the solution may compriseplate-shaped crystals. Since the plate-shaped crystals more easilydissolve into the solution which includes the alkaline metal as comparedto columnar crystals, the dissolving rate of the group III nitride ishigh, thereby enabling a stable supply of the raw material required forthe recrystallization. As a result, it is possible to grow a practicallylarge group III nitride crystal having a high quality.

The group III nitride which is dissolved into the solution may comprisean approximately stoichiometry composition. If the group III nitride rawmaterial greatly deviates from the stoichiometry composition, thecrystal growth rate may decrease and the grown crystal may deviate fromthe stoichiometry composition to deteriorate the crystal quality.Accordingly, by dissolving the group III nitride having an approximatelystoichiometry composition into the solution which includes the alkalinemetal, it is possible recrystallize and grow the group III nitridecrystal having an approximately stoichiometry composition.

The group III nitride which is dissolved into the solution may comprisegroup III nitride crystals which are grown from a material whichcomprises nitrogen and a mixture of an alkaline metal and a group IIImetal. In this case, the nitrogen defect can be reduced, and it ispossible to grow a high purity group III nitride crystal having anapproximately stoichiometry composition. As a result, it is possible togrow a practically large group III nitride crystal having a highquality.

The group III nitride crystal may be grown on a seed crystal. In thiscase, it is possible to grow a practically large group III nitridecrystal having a high quality.

Fourteenth Embodiment

A fourteenth embodiment of the method of growing the group III nitridecrystal forms, within a reaction chamber, a molten mixture of analkaline metal and a material which includes a group III metal, grows agroup III nitride crystal which is made of the group III metal andnitrogen, from the molten mixture and a material which includes thenitrogen, and controls a temperature in a vicinity of a surface of themolten mixture and a temperature of a crystal growing region within themolten mixture, so that the nitrogen dissolves into the molten mixturefrom the surface and the group III nitride crystal grows in the crystalgrowing region which is other than the surface.

The group III metal may be selected from Ga, Al, In and the like. Inaddition, the alkaline metal may be selected from K, Na and the like. Inaddition, the material which includes nitrogen may be any suitablecompound including nitrogen, such as nitrogen (N₂) gas, sodium azide(NaN₃), and ammonia (NH₃).

As long as the temperature in the vicinity of the surface of the moltenmixture and the temperature of the crystal growing region arecontrolled, the two temperatures may be the same or mutually differenttemperatures.

Therefore, it is possible to grow a large group III nitride crystalunder a crystal growing temperature condition that generates no nucleusof the group III nitride crystal in the vicinity of the surface of themolten mixture, that is, by growing the group III nitride crystal in thecrystal growing region which is other than the surface of the moltenmixture.

FIG. 19 is a cross sectional view showing a fourteenth embodiment of thegroup III nitride crystal growing apparatus according to the presentinvention. The group III nitride crystal growing apparatus shown in FIG.19 includes a reaction chamber 1101, and a solution container 1102 whichis provided within the reaction chamber 1101. The solution container1102 contains a molten mixture 1103 which includes Ga and Na. In thisembodiment, the Ga is used as the material which includes the group IIImetal, and the Na is used as the alkaline metal. The alkaline metal,namely, the Na, may be supplied from outside the reaction chamber 1101or, initially provided within the solution container 1102.

A lid 1109 is provided on top of the solution container 1102, and a gapis provided between the solution container 1102 and the lid 109 forallowing gas input and output with respect to the solution container1102. The reaction chamber 1101 is made of stainless steel, for example.On the other hand, the solution container 1102 is made of BN, AlN orpyrolitic BN.

A first heater 1106 and a second heater 1107 are provided on the outerside of the solution container 1102, so that the group III nitride (GaN)may be controlled to the crystal growing temperature. The first heater1106 is disposed under the second heater 1107, so that the second heater1107 mainly heats the upper portion of the solution container 1102 andthe first heater 1106 mainly heats the lower portion of the solutioncontainer 1102.

A first temperature sensor 1112 for detecting the temperature at thelower portion of the solution container 1102 is provided at the lowerportion of the solution container 1102. A second temperature sensor 1113for detecting the temperature at the upper portion of the solutioncontainer 1102 is provided at the upper portion of the solutioncontainer 1102. An output of the first temperature sensor 1112 iscoupled to the first heater 1106 to enable a feedback control of thefirst heater 1106, so that the lower portion of the solution container1102 is controlled to a desired temperature. Similarly, an output of thesecond temperature sensor 1113 is coupled to the second heater 1107 toenable a feedback control of the second heater 1107, so that the upperportion of the solution container 1102 is controlled to a desiredtemperature.

The material which includes nitrogen may be N₂ gas. In FIG. 19, a N₂ gascontainer 1114 which contains the N₂ gas is provided outside thereaction chamber 1101. The N₂ gas from the N₂ gas container 1114 can besupplied to a space 1108 within the reaction chamber 1101 via a gassupply pipe 1104. In this embodiment, the N₂ gas is supplied from alower portion of the reaction chamber 1101. In order to adjust thepressure of the N₂ gas, a pressure gage 1111 is provided to detect thepressure of the N₂ gas within the reaction chamber 1101, and a pressureadjusting valve 1105 is provided to adjust the pressure of the N₂ gasvia the gas supply pipe 1104. An output of the pressure gage 1111 iscoupled to the pressure adjusting valve 1105 to enable a feedbackcontrol of the pressure adjusting valve 1105, so that the pressurewithin the reaction chamber 1101 is controlled to a desired pressure.

In this embodiment, the N₂ pressure within the reaction chamber 1101 isset to 3 MPa, the temperature at the upper portion of the solutioncontainer 1102 is set to 1000° C., the temperature at the lower portionof the solution container 1102 is set to 850° C., and a seed crystal isinitially set in the lower portion of the solution container 1102. Inthis state, the above described pressure and temperatures aremaintained, so that a GaN crystal 1110 grows on the nucleus of the seedcrystal.

The GaN crystal 1110 does not grow at the surface of the molten mixture1103, and the GaN crystal 1110 grows only in the crystal growing regionat the lower portion of the solution container 1102 where the seedcrystal is set. The nitrogen dissolves into the molten mixture 1103 fromthe surface of the molten mixture 1103, and the GaN crystal 1110 growsonly in the crystal growing region where the seed crystal is set.

Because the crystal growth does not occur at the surface of the moltenmixture 1103 and the crystal growth occurs only in the intended crystalgrowing region, the raw material is efficiently utilized, and ahigh-quality GaN crystal can be grown by controlling the generation ofthe nucleus of the GaN.

FIG. 20 is a perspective view showing a columnar GaN crystal which isobtained by growing the GaN crystal by the group III nitride crystalgrowing apparatus shown in FIG. 19.

When a GaN crystal 1301 shown in FIG. 20 is set as the seed crystal atthe lower portion of the solution container 1102, the GaN crystal growson the GaN seed crystal 1301 by maintaining the crystal growthconditions described above, and a columnar GaN crystal 1302 is obtained.

The GaN seed crystal 1301 has a hexagonal column shape, and thus, ahexagonal columnar GaN crystal 1302 is grown on the GaN seed crystal1301. In FIG. 20, top and bottom surfaces of the hexagonal column shapeare the c-plane.

FIG. 21 is a diagram showing a relationship between a crystal growingtemperature and a crystal growing pressure for the group III nitridecrystal. In FIG. 21, the ordinate indicates the N₂ pressure (P) withinthe reaction chamber 1101 in MPa, and the abscissa indicates the inverseof the absolute temperature (1/T) of the molten mixture 1103 in “×10⁻³K⁻¹”. Different crystal forms are obtain in four regions A, B, C and Dshown in FIG. 21.

In the region A, no group III nitride crystal grows and the group IIInitride crystal decomposes. In the region B, the group III nitridecrystal grows only on the seed crystal, and no group III nitride crystalgrows on the inner walls or the like of the solution container 1102 (orreaction chamber 1101). In the regions C and D, the nucleus of the groupIII nitride is naturally generated, and the group III nitride crystalalso grows on the inner walls and the like of the solution container1102 (or reaction chamber 1101). The columnar crystal grows dominantlyin the region C, while the plate-shaped crystal grows dominantly in theregion D.

In this embodiment, the temperature and pressure at the surface of themolten mixture 1103 correspond to those in the region A shown in FIG.21. On the other hand, the temperature and pressure at the lower portionof the solution container 1102 where the seed crystal is set correspondto those in the region B shown in FIG. 21.

Because the crystal growth occurs dominantly on the seed crystal in theregion B shown in FIG. 21, the crystal growth is unlikely to newly occurin regions other than that of the seed crystal, thereby enablingefficient utilization of the raw material. In other words, virtually allof the raw material is used by the GaN crystal which grows on the seedcrystal, and the Ga which is initially prepared and set in the solutioncontainer 1102 is efficiently utilized. As a result, it is possible togrow a large GaN crystal without having to use a large amount of Ga.

In addition, the crystal orientation of the group III nitride crystalcan easily be controlled, because the group III nitride crystal can begrown on the seed crystal. In other words, by using as the seed crystala GaN crystal or the like having a predetermined crystal orientation, itis possible to accurately control the crystal orientation of the groupIII nitride crystal which is grown. As a result, when finally slicingthe group III nitride crystal which is obtained, it is possible toeasily obtain the desired crystal

orientation. Hence, a GaN substrate obtained with the desired crystal othe GaN crystal which is obtained.

Therefore, according to this possible to obtain a group III nitri highquality and low defect density.

In FIG. 20, the GaN seed the hexagonal column shape. However, the seedcrystal may have other shapes, such as a plat described later inconjunction with embodiment. Furthermore, the group may be grown on anepitaxial layer possible to obtain a large plate-shaped nitride crystalsuch as the GaN

Fifteenth Embodiment

A fifteenth embodiment o growing the group III nitride crystalfourteenth embodiment described ab within the reaction chamber by themat includes the nitrogen and in a gas controls a pressure within thereac a partial pressure of the material w nitrogen and is in the gaseousstate nucleus of the group III nitride in surface in response to atemperature surface. The space within the reaction chamber may include agas other than the material which includes the nitrogen.

The temperature and pressure at the surface of the molten mixture areset to those of the region A or B shown in FIG. 21, and temperature andpressure in the region other than the surface of the molten mixture areset to those of the region B or C or D shown in FIG. 21 so that thecrystal growth occurs in the region.

The group III nitride crystal does not grow at the surface of the moltenmixture, and the nitrogen dissolves into the molten mixture from thesurface of the molten mixture. The nitrogen which dissolves into themolten mixture diffuses to the region other than the surface of themolten mixture, and the group III nitride crystal grows under thepressure and temperature conditions of the region B or C or D shown inFIG. 21.

Therefore, the pressure and the atmosphere can be controlled with easeaccording to this embodiment. Moreover, by setting the partial pressureof the material (gas) which includes the nitrogen to a constant valueand generating a temperature change, it becomes easy to dissolve thenitrogen into the molten mixture from the surface of the molten mixtureand to grow the group III nitride crystal in the region other than thesurface of the molten mixture.

A fifteenth embodiment of the group III nitride crystal growingapparatus may have the same structure as that shown in FIG. 19, butoperated under different conditions. In this embodiment, the N₂ pressurewithin the reaction chamber 1101 is set to 3 MPa, the temperature at theupper portion of the solution container 1102 is set to 1000° C., and thetemperature at the lower portion of the solution container 1102 is setto 800° C. In this state, the above described pressure and temperaturesare maintained, so that a GaN crystal 1110 grows at the lower portion ofthe solution container 1102.

In this case, the GaN crystal 1110 does not grow at the surface of themolten mixture 1103, and the GaN crystal 1110 grows only at the lowerportion of the solution container 1102. The nitrogen dissolves into themolten mixture 1103 from the surface of the molten mixture 1103, and theGaN crystal grows only at the lower portion of the solution container1102. In this state, a columnar GaN crystal 1401A shown in FIG. 22 or acolumnar GaN crystal 1401B shown in FIG. 23 grows dominantly at thelower portion of the solution container 1102. FIG. 22 is a perspectiveview showing the columnar GaN crystal 1401A which may be obtained bygrowing the GaN crystal by this fifteenth embodiment, and FIG. 23 is aperspective view showing the columnar GaN crystal 1401B which may beobtained by this embodiment.

The columnar GaN crystal 1401A shown in FIG. 22 has a hexagonal columnshape, while the columnar GaN crystal 1401B shown in FIG. 23 has shapewhich is a combination of a hexagonal column shape with a hexagonalpyramid shape on top. In FIGS. 22 and 23, bottom surfaces of thehexagonal column shapes of the columnar GaN crystals 1401A and 1401B arethe c-plane. In other words, the columnar GaN crystals 1401A and 1401Bshown in FIGS. 22 and 23 extend in the c-axis direction.

Since this embodiment does not grow the GaN crystal at the surface ofthe molten mixture 1103 and grows the GaN crystal only in thepredetermined intended region, the raw material is efficiently utilized,and a high-quality GaN crystal can be grown by controlling the nucleusgeneration.

In this embodiment, the temperature and pressure at the surface of themolten mixture 1103 correspond to those of the region A shown in FIG.21, and the temperature and pressure at the lower portion of the moltenmixture 1103 where the GaN crystal grows correspond to those of theregion C shown in FIG. 21.

Because the columnar GaN crystal grows dominantly in the region C shownin FIG. 21, the crystal orientation is definite. Hence, when making aGaN substrate from the columnar GaN crystal, it is easy to determine thecrystal orientation and the slicing of the columnar GaN crystal.

In addition, since the columnar GaN crystal grows from the naturalnucleus generation in the region C shown in FIG. 21, even when there isno seed crystal, it is possible to use the columnar GaN crystal which isgrown in the region C as the seed crystal which is used in the region B.

Sixteenth Embodiment

A sixteenth embodiment of the method of growing the group III nitridecrystal is based on the fourteenth embodiment described above, and thetemperature in the vicinity of the surface of the molten mixture iscontrolled to a temperature which is higher than the temperature of thecrystal growing region. In other words, the group III nitride crystal isgrown in the region having a lower temperature than the surface of themolten mixture, and the group III nitride crystal is not grown at thesurface of the molten mixture. The temperature is higher towards theleft side along the abscissa in FIG. 21.

According to this embodiment, it is possible to set a large margin forthe crystal growing conditions. That is, since the region A shown inFIG. 21 becomes the higher temperature region and it is easy to set theregions. B, C and D as the lower temperature regions having a lowertemperature than the region A, it is possible to set a large margin forthe crystal growing conditions. As a result, it is possible to growgroup III nitride crystals having various forms, as will be describedlater.

A sixteenth embodiment of the group III nitride crystal growingapparatus may have the same structure as that shown in FIG. 19, butoperated under different conditions. In this embodiment, the N₂ pressurewithin the reaction chamber 1101 is set to 3

MPa, the temperature at the upper portion of the solution container 1102is set to 1000° C., and the temperature at the lower portion of thesolution container 1102 is set to 730° C. In this state, the abovedescribed pressure and temperatures are maintained, so that a GaNcrystal 1110 grows at the lower portion of the solution container 1102.

In this case, the GaN crystal 1110 does not grow at the surface of themolten mixture 1103, and the GaN crystal 1110 grows only at the lowerportion of the solution container 1102. The nitrogen dissolves into themolten mixture 1103 from the surface of the molten mixture 1103, and theGaN crystal grows only at the lower portion of the solution container1102. In this state, a plate-shaped GaN crystal 1501 shown in FIG. 24grows dominantly at the lower portion of the solution container 1102.FIG. 24 is a perspective view showing the plate-shaped GaN crystal 1501which is obtained by growing the GaN crystal by this sixteenthembodiment.

The group III nitride crystal which is grown by this sixteenthembodiment is not limited to the hexagonal plate-shaped GaN crystal 1501shown in FIG. 24, and group III nitride crystals having shapes otherthan the hexagonal plate shape may be grown. For example, a polygonalplate-shaped group III nitride crystal of the hexagonal system may begrown by this embodiment. In each case, the plate-shaped group IIInitride crystal extends parallel to the (0001) face, that is, thec-plane.

Since this embodiment does not grow the GaN crystal at the surface ofthe molten mixture 1103 and grows the GaN crystal only in thepredetermined intended region, the raw material is efficiently utilized,and a high-quality GaN crystal can be grown by controlling the nucleusgeneration.

In this embodiment, the temperature and pressure at the surface of themolten mixture 1103 correspond to those of the region A shown in FIG.21, and the temperature and pressure at the lower portion of the moltenmixture 1103 where the GaN crystal grows correspond to those of theregion D shown in FIG. 21.

Because the plate-shaped GaN crystal grows dominantly in the region Dshown in FIG. 21, the plate-shaped GaN crystal may be used as it is as aGaN substrate. Furthermore, even when undulations are formed on thesurface of the plate-shaped GaN crystal, the surface undulations can beeliminated by simply polishing the crystal surface so that theplate-shaped GaN crystal may be used as the GaN substrate.

The crystal growth rate in the in-plane direction of the plate-shapedgroup III nitride crystal is high in the region D shown in FIG. 21. Forthis reason, the GaN crystal can be grown efficiently at a low cost.

In addition, since the plate-shaped GaN crystal grows from the naturalnucleus generation in the region D shown in FIG. 21, even when there isno seed crystal, it is possible to use the plate-shaped GaN crystalwhich is grown in the region D as the seed crystal which is used in theregion B.

Seventeenth Embodiment

A seventeenth embodiment of the method of growing the group III nitridecrystal is based on the sixteenth embodiment described above, and sets aseed crystal in the crystal growing region, and controls the temperatureand a pressure in the crystal growing region, so that the group IIInitride crystal grows on the seed crystal.

More particularly, the temperature and pressure of the region where theseed crystal is set are controlled to be those of the region B shown inFIG. 21. On the other hand, the temperature and pressure at the surfaceof the molten mixture are controlled to be those of the region A shownin FIG. 21. Under these crystal growing conditions, the nitrogendissolves into the molten mixture from the surface of the moltenmixture, and the group III nitride crystal grows only on the seedcrystal which is set in the region described above.

The seed crystal may be made of any group III nitride, as long as itfunctions as a seed crystal. Hence, the seed crystal may be made of thesame material as the group III nitride crystal which grows in the moltenmixture or, may be made of a material different from that of the groupIII nitride crystal which grows in the molten mixture. Although thegroup III nitride crystal grows on the seed crystal even when the seedcrystal is made of the material which is different from that of thegroup III nitride crystal which grows in the molten mixture, it isdesirable from the point of view of obtaining a high quality crystalthat the seed crystal is made of the same material as the group IIInitride crystal which grows in the molten mixture.

Since the group III nitride crystal does not grow at the surface of themolten mixture and grows only in the intended predetermined region ofthe molten mixture, the raw material is efficiently utilized, and ahigh-quality crystal can be grown by controlling the nucleus generation.

Because the crystal growth occurs dominantly on the seed crystal in theregion B shown in FIG. 21, the crystal growth is unlikely to newly occurin regions other than that of the seed crystal, thereby enablingefficient utilization of the raw material. In other words, virtually allof the raw material is used by the group III nitride (GaN) crystal whichgrows on the seed crystal, and the group III metal (Ga) which isinitially prepared and set in the solution container 1102 is efficientlyutilized. As a result, it is possible to grow a large group III nitride(GaN) crystal without having to use a large amount of group III metal(Ga).

In addition, the crystal orientation of the group III nitride crystalcan easily be controlled, because the group III nitride crystal can begrown on the seed crystal. In other words, by using as the seed crystala GaN crystal or the like having a predetermined crystal orientation, itis possible to accurately control the crystal orientation of the groupIII nitride crystal which is grown. As a result, when finally slicingthe group III nitride crystal which is obtained, it is possible toeasily obtain the desired crystal orientation. Hence, a GaN substrate orthe like can be obtained with the desired crystal orientation by slicingthe GaN crystal which is obtained.

Therefore, according to this embodiment, it is possible to obtain agroup III nitride crystal having a high quality and low defect density.

A seventeenth embodiment of the group III nitride crystal growingapparatus may have the same structure as that shown in FIG. 19, butoperated under different conditions. In this embodiment, the N₂ pressurewithin the reaction chamber 1101 is set to 2 MPa, the temperature at theupper portion of the solution container 1102 is set to 850° C., and thetemperature at the lower portion of the solution container 1102 is alsoset to 850° C. Further, a seed crystal is initially prepared and set inthe lower portion of the solution container 1102. In this state, theabove described pressure and temperatures are maintained, so that a GaNcrystal 1110 grows at the lower portion of the solution container 1102using the seed crystal as the nucleus.

Although the seed crystal is set in the lower portion of the solutioncontainer 1102, that is, the lower portion of the molten mixture 1103,it is of course possible to obtain similar effects by setting the seedcrystal on the side wall or the like of the solution container 1102.

The effects obtainable in this embodiment are basically the same asthose obtainable by the fourteenth embodiment described above, exceptthat the temperatures of the upper and lower portions of the solutioncontainer 1102 are set to the same temperature in this embodiment. Andsince the temperatures at the upper and lower portions of the solutioncontainer 1102 are the same, the temperature of the entire moltenmixture 1103 becomes uniform, and the thermal deviation becomes small,thereby making it possible to grow the group III nitride (GaN) crystalunder stable crystal growing conditions.

Eighteenth Embodiment

An eighteenth embodiment of the method of growing the group III nitridecrystal is based on the sixteenth embodiment described above, andcontrols the temperature and a pressure in the crystal growing region,so that a columnar group III nitride crystal grows in the crystalgrowing region.

More particularly, the temperature and pressure in the region within themolten mixture where the columnar group III nitride crystal grows arecontrolled to those of the region C shown in FIG. 21. On the other hand,the temperature and pressure at the surface of the molten mixture arecontrolled to those of the region A or B shown in FIG. 21. Hence, thegroup III nitride crystal does not grow at the surface of the moltenmixture, and the nitrogen dissolves into the molten mixture from thesurface of the molten mixture. In other words, the columnar group IIInitride crystal grows because the temperature and pressure arecontrolled to those of the region C shown in FIG. 21 only in the regionwithin the molten mixture where the columnar group III nitride crystalgrows.

Since this embodiment does not grow the GaN crystal at the surface ofthe molten mixture 1103 and grows the GaN crystal only in thepredetermined intended region, the raw material is efficiently utilized,and a high-quality GaN crystal can be grown by controlling the nucleusgeneration.

Moreover, because the columnar GaN crystal grows dominantly in theregion C shown in FIG. 21, the crystal orientation is definite. Hence,when making a GaN substrate from the columnar GaN crystal, it is easy todetermine the crystal orientation and the slicing of the columnar GaNcrystal.

An eighteenth embodiment of the group III nitride crystal growingapparatus may have the same structure as that shown in FIG. 19, butoperated under different conditions. In this embodiment, the N₂ pressurewithin the reaction chamber 1101 is set to 2 MPa, the temperature at theupper portion of the solution container 1102 is set to 800° C., and thetemperature at the lower portion of the solution container 1102 is setto 850° C. Further, a seed crystal is initially prepared and set in thelower portion of the solution container 1102. In this state, the abovedescribed pressure and temperatures are maintained, so that a GaNcrystal 1110 grows at the lower portion of the solution container 1102using the seed crystal as the nucleus.

Although the seed crystal is set in the lower portion of the solutioncontainer 1102, that is, the lower portion of the molten mixture 1103,it is of course possible to obtain similar effects by setting the seedcrystal on the side wall or the like of the solution container 1102.

The effects obtainable in this embodiment are basically the same asthose obtainable by the fourteenth or seventeenth embodiment describedabove, except that the temperature of the upper portion of the solutioncontainer 1102 is lower than the temperature of the lower portion of thesolution container 1102 in this embodiment. And since the temperaturesat the upper and lower portions of the solution container 1102 aredifferent, convection of the molten mixture 1103 occurs, therebyscattering the nitrogen which dissolves into the molten mixture 1103from the surface of the molten mixture 1103, throughout the entiremolten mixture 1103, to realize a uniform nitrogen concentration. As aresult, it is possible to realize a stable growth of the GaN crystal.

Although N₂ gas is used as the material which includes nitrogen, it isalso possible to supply to the reaction chamber 1101 other materialswhich include the nitrogen, such as sodium azide (NaN₃), and ammonia(NH₃) gas.

It is also possible to supply to the reaction chamber 1101 a gas mixtureof the material which includes the nitrogen and an inert gas such as Argas, where the material which includes the nitrogen may be nitrogen (N₂)gas, sodium azide (NaN₃) or ammonia (NH₃) gas. The inert gas that isused does not react with the alkaline metal, the material which includesthe group III metal or the material which includes the nitrogen.

Even in the case where the gas mixture of the material which includesthe nitrogen (nitrogen (N₂) gas, sodium azide (NaN₃) or ammonia (NH₃)gas) and the inert gas (Ar gas) is supplied to the reaction chamber1101, the pressure at which the group III nitride crystal is grown isdetermined by the effective N₂ gas pressure within the reaction chamber1101, and not the total pressure of the gas mixture.

Nineteenth Embodiment

A nineteenth embodiment of the method of growing the group III nitridecrystal is based on the sixteenth embodiment described above, andcontrols the temperature and a pressure in the crystal growing region,so that a plate-shaped group III nitride crystal grows in the crystalgrowing region.

More particularly, the temperature and pressure in the region within themolten mixture where the plate-shaped group III nitride crystal growsare controlled to those of the region D shown in FIG. 21. On the otherhand, the temperature and pressure at the surface of the molten mixtureare controlled to those of the region A or B shown in FIG. 21. Hence,the group III nitride crystal does not grow at the surface of the moltenmixture, and the nitrogen dissolves into the molten mixture from thesurface of the molten mixture. In other words, the plate-shaped groupIII nitride crystal grows because the temperature and pressure arecontrolled to those of the region D shown in FIG. 21 only in the regionwithin the molten mixture where the plate-shaped group III nitridecrystal grows.

Since this embodiment does not grow the GaN crystal at the surface ofthe molten mixture 1103 and grows the GaN crystal only in thepredetermined intended region, the raw material is efficiently utilized,and a high-quality GaN crystal can be grown by controlling the nucleusgeneration.

Moreover, because the plate-shaped GaN crystal grows dominantly in theregion D shown in FIG. 21, the plate-shaped GaN crystal may be used asit is as a GaN substrate. Furthermore, even when undulations are formedon the surface of the plate-shaped GaN crystal, the surface undulationscan be eliminated by simply polishing the crystal surface so that theplate-shaped GaN crystal may be used as the GaN substrate.

The crystal growth rate in the in-plane direction of the plate-shapedgroup III nitride crystal is high in the region D shown in FIG. 21. Forthis reason, the GaN crystal can be grown efficiently at a low cost.

Twentieth Embodiment

A twentieth embodiment of the method of growing the group III nitridecrystal is based on the sixteenth embodiment described above, andlocates the crystal growing region in a lower portion of the reactionchamber.

The lower portion of the reaction chamber refers to a region which islower than the surface of the molten mixture from which the nitrogendissolves into the molten mixture.

According to this embodiment, a large group III nitride crystal can begrown continuously within the molten mixture. In other words, stablecrystal growing conditions are obtained in the molten mixture, such assmall temperature deviation and a constant ratio of raw materials,thereby making it possible to grow a large group III nitride crystalhaving a high quality.

Twenty-First Embodiment

A twenty-first embodiment of the method of growing the group III nitridecrystal is based on the fourteenth embodiment described above, andcontrols the temperature in the vicinity of the surface of the moltenmixture and the temperature of the crystal growing region toapproximately same temperature.

More particularly, the temperature and pressure of the region within themolten mixture 1103 where the group III nitride crystal grows are set tothose of the region B shown in FIG. 21, and the group III nitridecrystal grows only on the seed crystal. Since the pressure of thematerial (gas) including nitrogen is approximately constant within thereaction chamber 1101, the temperature in the vicinity of the surface ofthe molten mixture 1103 and the temperature of the crystal growingregion within the molten mixture 1103 may be regarded as beingapproximately the same as long as the temperatures are controlled withinthe temperature range of the region B shown in FIG. 21.

Therefore, according to this embodiment, the temperature within theentire molten mixture becomes uniform and the thermal deviation becomessmall, because the temperature in the vicinity of the surface of themolten mixture and the temperature of the crystal growing region arecontrolled to approximately the same temperature. Hence, the group IIInitride crystal can be grown under stable crystal growing conditions. Asa result, it is possible to grow a large group III nitride crystalhaving a high quality.

Twenty-Second Embodiment

A twenty-second embodiment of the method of growing the group IIInitride crystal is based on the fourteenth embodiment described above,and controls the temperature in the vicinity of the surface of themolten mixture to a temperature which is lower than a temperature at alower portion of the molten mixture within the reaction chamber.

More particularly, the lower portion of the molten mixture 1103 refersto a portion lower than the vicinity of the surface of the moltenmixture 1103. The temperature and pressure of the region within themolten mixture 1103 where the group III nitride crystal grows are set tothose of the region B shown in FIG. 21, and the group III nitridecrystal grows only on the seed crystal.

Therefore, according to this embodiment, convection is generated in themolten mixture, because the temperature in the vicinity of the surfaceof the molten mixture is controlled to be lower than the temperature ofthe lower portion of the molten mixture. Hence, the convection of themolten mixture scatters the nitrogen which dissolves into the moltenmixture from the surface of the molten mixture, to make the nitrogenconcentration uniform within the entire molten mixture. As a result, thegroup III nitride crystal can be grown under stable crystal growingconditions, and it is possible to grow a large group III nitride crystalhaving a high quality.

According to the fourteenth through twenty-second embodiments, it ispossible to improve the positional controllability and the growthparameter controllability, and to efficiently dissolve the nitrogen intothe molten mixture and to efficiently utilize the group III metal, so asto grow a large group III nitride crystal.

Embodiments of Semiconductor Device

FIG. 25 is a perspective view showing an important part of a firstembodiment of a semiconductor device according to the present invention.This embodiment of the semiconductor device uses a GaN substrate whichis obtained by any of the above described embodiments of the method ofgrowing the group III nitride crystal or the group III nitride crystalgrowing apparatus. For the sake of convenience, it is assumed that theGaN substrate used is obtained by the group III nitride crystal growingapparatus shown in FIG. 19.

A semiconductor laser shown in FIG. 25 has an n-type GaN substrate 601which is obtained by the group III nitride crystal growing apparatusshown in FIG. 19. An n-type AlGaN clad layer 602, an n-type GaN guidelayer 603, an InGaN Multi-Quantum-Well (MQW) active layer 604, a p-typeGaN guide layer 605, a p-type AlGaN clad layer 606 and a p-type GaNcontact layer 607 are successively stacked on the n-type GaN substrate601. The layers on the n-type GaN substrate 601 may be formed by thinfilm crystal growing techniques such as Metal Organic Vapor PhaseEpitaxy (MO-VPE) and Molecular Beam Epitaxy (MBE).

A ridge structure is formed by the stacked layers of GaN, AlGaN andInGaN, and a SiO₂ insulator layer 608 has a hole at the p-type GaNcontact layer 607. A p-type (Au/Ni) ohmic electrode 609 and an n-type(Al/Ti) ohmic electrode 610 are respectively disposed on top and bottomof the semiconductor laser.

By applying a voltage across the p-type ohmic electrode 609 and then-type ohmic electrode 610 to supply a current to the semiconductorlaser, the semiconductor laser oscillates and emits a laser beam in adirection of an arrow shown in FIG. 25.

The crystal defects within the semiconductor laser are reduced becausethe crystal detects of the n-type GaN substrate 601 are reduced.Consequently, the semiconductor laser can operate for a long serviceablelife to produce a large output. In addition, since the GaN substrate 601used is the n-type, it is possible to form the ohmic electrode 610directly on the GaN substrate 601 and to reduce the cost, unlike theconventional insulative substrate such as a sapphire substrate whichrequires two electrodes to be drawn out from the p and n sides via agroup III nitride crystal layer which is grown on the sapphiresubstrate. Moreover, a light emission end surface of the semiconductorlaser can be formed by cleaving, when cleaving the chips, thereby makingit possible to realize a high-quality semiconductor laser at a low cost.

In FIG. 25, an InGaN MQW is used as the active layer 604. However, it ispossible to use an AlGaN MQW as the active layer 604, so as to shortenthe light emission wavelength. In other words, because the crystaldefects and impurities in the GaN substrate 601 are small, lightemission from a deep level decreases, and a highly efficientsemiconductor laser can be realized even when the light emissionwavelength is shortened.

Of course, the use of the GaN substrate is not limited to opticaldevices such as the semiconductor laser, and the GaN substrate issimilarly applicable to electronic devices. In other words, by use ofthe GaN substrate having the reduced crystal defects, GaN-based layersgrown epitaxially on the GaN substrate also have reduced crystaldefects. As a result, it is possible to realize a high-performancedevice by suppressing a leak current and improving the carrier trappingeffect when the well structure is employed.

Therefore, high-performance devices can be realized by the use of thegroup III nitride substrate which is obtained by the method or apparatusof growing the group III nitride crystal. In the case of semiconductorlasers and light emitting diodes, “high-performance” includes highoutput and long serviceable life which could not be realizedconventionally. On the other hand, in the case of electronic devices,“high-performance” includes low power consumption, low noise, high-speedoperation and operability under high-temperature conditions.Furthermore, in the case of light receiving devices, “high-performance”includes low noise and long serviceable life.

FIG. 26 is a perspective view showing an important part of a secondembodiment of the semiconductor device according to the presentinvention, and FIG. 27 is a cross sectional view showing an importantpart of the semiconductor device shown in FIG. 26 cut along a planeperpendicular to a light emitting direction. This embodiment of thesemiconductor device Uses a GaN substrate which is obtained by any ofthe above described embodiments of the method of growing the group IIInitride crystal or the group III nitride crystal growing apparatus. Forthe sake of convenience, it is assumed that the GaN substrate used isobtained by the group III nitride crystal growing apparatus shown inFIG. 10.

A semiconductor laser shown in FIGS. 26 and 27 has an n-type GaNsubstrate 750 which has a thickness of 250 μm and is obtained by thegroup III nitride crystal growing apparatus shown in FIG. 10. A stackedstructure 2400 shown in FIG. 26 includes an n-type GaN layer 740, ann-type Al_(0.2)Ga_(0.8) clad layer 741, an n-type GaN guide layer 742,an In_(0.05)Ga_(0.95)N/In_(0.15)Ga_(0.85)N MQW activation layer 743, ap-type GaN guide layer 744, a p-type Al_(0.2)Ga_(0.8)N clad layer 745and a p-type GaN cap layer 746 which are successively stacked on the topsurface of the n-type GaN substrate 750 by Metal Organic Chemical VaporDeposition (MOCVD), as shown in FIG. 27.

The stacked structure 2400 is etched from the p-type GaN cap layer 746to a portion of the p-type Al_(0.2)Ga_(0.8)N clad layer 745 so that astripe-shaped portion remains, to thereby form a current-narrowing ridgewaveguide structure 751. The ridge waveguide structure 751 is formedalong the <1-100> direction of the n-type GaN substrate 750, where<1-100> denotes <“1” “1 bar” “0” “0”>. A SiO₂ insulator layer 747 isformed on the surface of the stacked structure 2400. An opening isformed in the SiO₂ insulator layer 747 on a ridge 751.

A p-side ohmic electrode 748 is formed on the surface of the p-type GaNcap layer 746 which is exposed via this opening in the SiO₂ insulatorlayer 747. An n-side ohmic electrode 749 is formed on the bottom surfaceof the n-type GaN substrate 750. The p-side ohmic electrode 748 and then-side ohmic electrode 749 may be formed by vapor deposition of Ni/Auand Ti/Al, respectively.

Optical resonator surfaces 2401 and 2402 are formed perpendicularly tothe ridge 751 and the In_(0.05)Ga_(0.95)N/In_(0.95)Ga_(0.85)N MQWactivation layer 743. The optical resonator surfaces 2401 and 2402 areformed by forming a cleavage of a (1-100) face which is perpendicular tothe ridge waveguide structure 751 which extends in the <1-100> directionof the n-type GaN substrate 750. The n-side ohmic electrode 749 and theoptical resonator surfaces 1401 and 1402 are formed by polishing thebottom surface of the n-type GaN substrate 750 to a thickness of 80 μm.

By applying a voltage across the p-side ohmic electrode 748 and then-side ohmic electrode 549, a current flows to inject carriers into theIn_(0.05)Ga_(0.95)N/In_(0.15)Ga_(0.85)N MQW activation layer 743. As aresult, light emission and light amplification occur, and laser beams1411 and 1412 are emitted from respective optical resonator surfaces1401 and 1402, as indicated by arrows in FIG. 26.

The present inventors confirmed that the semiconductor laser has a longserviceable life even when operated to produce a high output, becausethe crystal defects in the semiconductor laser of this embodiment issmall and the crystal quality of the layers formed on the group IIInitride substrate is high, compared to the case where the conventionalsapphire substrate or, a GaN substrate which is obtained by theconventional technique such as vapor deposition is used for thesemiconductor laser.

FIG. 28 is a cross sectional view showing an important part of a thirdembodiment of the semiconductor device according to the presentinvention. This embodiment of the semiconductor device uses a GaNsubstrate which is obtained by any of the above described embodiments ofthe method of growing the group III nitride crystal or the group IIInitride crystal growing apparatus. For the sake of convenience, it isassumed that the GaN substrate used is obtained by the group III nitridecrystal growing apparatus shown in FIG. 10.

A light receiving element shown in FIG. 28 has an n-type GaN substrate760 which has a thickness of 300 μm and is obtained by the group IIInitride crystal growing apparatus shown in FIG. 10. An n-type GaN layer761, an insulative GaN layer 762, and a transparent Schottky electrode763 made of Ni/Au are stacked on the top surface of the n-type GaNsubstrate 760, to form a Metal Insulator Semiconductor (MIS) type lightreceiving element. An ohmic electrode 764 made of Ti/Al is formed on thebottom surface of the n-type GaN substrate 760. Furthermore, an Auelectrode 765 is formed on a portion of the transparent Schottkyelectrode 763.

When light (ultraviolet ray) 2601 is received via the transparentSchottky electrode 763, carriers are generated to cause a photocurrentto flow via the electrodes 765 and 764.

The present inventors confirmed that the light receiving element has asmall dark current and a large signal-to-noise ratio (SNR), because thecrystal defects in the light receiving element of this embodiment issmall and the crystal quality of the layers formed on the group IIInitride substrate is high, compared to the case where the conventionalsapphire substrate or, a GaN substrate which is obtained by theconventional technique such as vapor deposition is used for the lightreceiving element.

FIG. 29 is a cross sectional view showing an important part of a fourthembodiment of the semiconductor device according to the presentinvention. This embodiment of the semiconductor device uses a GaNsubstrate which is obtained by any of the above described embodiments ofthe method of growing the group III nitride crystal or the group IIInitride crystal growing apparatus. For the sake of convenience, it isassumed that the GaN substrate used is obtained by the group III nitridecrystal growing apparatus shown in FIG. 10.

A High Electron Mobility Transistor (HEMT) shown in FIG. 29 forms anelectronic device having a high-resistance GaN substrate 770 which has athickness of 300 μm and is obtained by the group III nitride crystalgrowing apparatus shown in FIG. 10. An insulative GaN layer 771, ann-type AlGaN layer 772, and an n-type GaN layer 773 are stacked on thetop surface of the high-resistance GaN substrate 770, so as to form arecess gate type HEMT. A gate portion of the n-type GaN layer 773 isetched to the n-type AlGaN layer 772, and a gate electrode 776 made ofNi/Au is formed on the exposed n-type AlGaN layer 772. A drain electrode775 made of Ti/Al and a source electrode 774 made of Ti/Al are formed onthe n-type GaN layer 773 on respective sides of the gate electrode 776.

The present inventors confirmed that the HEMT has suppressed abnormaldiffusion and short-circuiting of the electrode which are caused bycrystal defects, high withstand voltage and satisfactory frequencycharacteristics, because the crystal defects in the HEMT of thisembodiment is small and the crystal quality of the layers formed on thegroup III nitride substrate is high, compared to the case where theconventional sapphire substrate or, a GaN substrate which is obtained bythe conventional technique such as vapor phase deposition is used forthe HEMT.

FIG. 30 is a diagram showing an illumination apparatus using a fifthembodiment of the semiconductor device according to the presentinvention, and FIG. 31 is a circuit diagram showing the illuminationapparatus shown in FIG. 30. FIG. 32 is a cross sectional view showing awhite LED module within the illumination apparatus shown in FIG. 30, andFIG. 33 is a cross sectional view showing an important part of the fifthembodiment of the semiconductor device within the white LED module.

The illumination apparatus shown in FIGS. 30 and 31 includes two whiteLED modules 1902, a current limiting resistor 796, a current source 797and a switch 798 which are connected in series. The white LED modules1902 are turned ON or OFF by switching the switch 798 to the ON or OFFstate.

As shown in FIG. 32, each white LED module 1902 has a YAG fluorescentmaterial 791 coated on an ultraviolet LED 790. When a predeterminedvoltage is applied across electrode terminals 794 and 795, theultraviolet LED 790 emits ultraviolet ray which excites the YAGfluorescent material 791 such that white light 1901 is emitted via theYAG fluorescent material 791. The white light 1901 is indicated byarrows in FIGS. 30 and 32.

The ultraviolet LED 790 shown in FIG. 33 has an n-type GaN substrate 780which has a thickness of 300 μm and is obtained by the group III nitridecrystal growing apparatus shown in FIG. 10. An n-type GaN layer 781, ann-type Al_(0.1)Ga_(0.9)N layer 782, an activation layer 783 having anInGaN/GaN MQW structure, a p-type Al_(0.1)Ga_(0.9)N layer 784, and ap-type GaN layer 785 are stacked on the top surface of the n-type GaNsubstrate 780. A transparent ohmic electrode 786 made of Ni/Au is formedon the p-type GaN layer 785. An electrode 787 made of Ni/Au and providedfor wire-bonding is formed on the transparent ohmic electrode 786. Inaddition, an ohmic electrode 788 made of Ti/Al is formed on the bottomsurface of the n-type GaN substrate 780.

By applying a voltage across the p-side electrode 787 and the n-sideohmic electrode 788, a current flows to inject carriers into theactivation layer 783. As a result, light emission occurs, andultraviolet ray 1801 is emitted from the ultraviolet LED 790, asindicated by an arrow in FIG. 33.

The present inventors confirmed that the LED has a high light emissionefficiency and is capable of producing a high output, because thecrystal defects in the LED of this embodiment is small and the crystalquality of the layers formed on the group III nitride substrate is high,compared to the case where the conventional sapphire substrate or, a GaNsubstrate which is obtained by the conventional technique such as vaporphase deposition is used for the LED.

In addition, it was confirmed that the illumination apparatus using theabove LED is brighter but has a low power, compared to the case wherethe conventional sapphire substrate or, a GaN substrate which isobtained by the conventional technique such as vapor phase deposition isused for the LED of the illumination apparatus.

Therefore, according to the embodiments of the semiconductor device, itis possible to realize high-performance semiconductor devices based onthe group III nitride substrate grown by the method or apparatus of thepresent invention, by providing a light emitting structure, a lightreceiving structure, a transistor structure and the like on the groupIII nitride substrate. In this case, the light emitting structure mayform a light emitting diode, a laser diode (semiconductor laser) and thelike. The light receiving structure may form a photoconductor cell, apn-junction photodiode, a hetero-junction photodiode, a hetero-junctionbipolar phototransistor and the like. The light receiving element may beused for a fire alarm sensor, a wavelength selection type detector andthe like. In addition, the transistor structure may form a Field EffectTransistor (FET), a Heterojunction Bipolar Transistor (HBT), HEMT andthe like. Of course, other electronic devices may be formed on the groupIII nitride substrate, such as high-temperature operating devices whichoperate at high temperatures, high-frequency devices which operate athigh frequencies, and electronic devices which produce a large output oroperate under a large power.

Further, the present invention is not limited to these embodiments, butvarious variations and modifications may be made without departing fromthe scope of the present invention.

1-49. (canceled)
 50. A crystal comprising: a group III nitride crystal;wherein the group III nitride crystal has a resistivity greater than orequal to 10⁴ Ωcm.
 51. The crystal as claimed in claim 50, wherein thegroup III nitride crystal has a length of approximately 5 mm or greater.52. The crystal as claimed in claim 51, wherein the group III nitridecrystal has a defect density, obtained by an etch pit densityevaluation, of 10⁶ cm⁻² or less.
 53. The crystal as claimed in claim 50,wherein the group III nitride crystal has a defect density, obtained byan etch pit density evaluation, of 10⁶ cm⁻² or less.
 54. The crystal asclaimed in claim 50, wherein the group III nitride crystal isplate-shaped or columnar.
 55. The crystal as claimed in claim 50,wherein the group III nitride crystal is semi-insulative.
 56. A groupIII nitride crystal structure comprising: a seed crystal; and thecrystal as claimed in claim 50 grown on the seed crystal.
 57. The groupIII nitride crystal structure as claimed in claim 56, wherein the groupIII nitride crystal is grown on a principal plane of a plate-shaped seedcrystal.
 58. The group III nitride crystal structure as claimed in claim57, wherein the plate-shaped seed crystal is a plate-shaped group IIInitride having a c-plane as the principal plane thereof.
 59. The groupIII nitride crystal structure as claimed in claim 56, wherein the groupIII nitride crystal has a length of approximately 5 mm or greater. 60.The group III nitride crystal structure as claimed in claim 59, whereinthe group III nitride crystal has a defect density, obtained by an etchpit density evaluation, of 10⁶ cm⁻² or less.
 61. The group III nitridecrystal structure as claimed in claim 56, wherein the group III nitridecrystal has a defect density, obtained by an etch pit densityevaluation, of 10⁶ cm⁻² or less.
 62. The group III nitride crystalstructure as claimed in claim 56, wherein the group III nitride crystalis plate-shaped or columnar.
 63. A semiconductor device comprising: asubstrate having a surface made of the crystal as claimed in claim 50;and a stacked structure provided on the surface of the substrate. 64.The semiconductor device as claimed in claim 63, wherein the stackedstructure includes a transistor structure.
 65. The semiconductor deviceas claimed in claim 63, wherein the group III nitride crystal has adefect density, obtained by an etch pit density evaluation, of 10⁶ cm⁻²or less.